This book documents the accomplishments of both the U.S. and the Mexican Boundary Commissions that mapped the boundary between 1849 and 1857.
The Treaty of Guadalupe Hildalgo, which officially ended the U.S.-Mexican War in 1848, cost Mexico half its territory, while the United States gained land that became California, Nevada, Utah, Texas, and parts of Colorado, Arizona, and New Mexico. Because the new United States-Mexico border ran through territory that was still incompletely mapped, the treaty also called for government commissions from both nations to locate and mark the boundary on the ground. This book documents the accomplishments of both the U.S. and the Mexican Boundary Commissions that mapped the boundary between 1849 and 1857, as well as the fifty-four pairs of maps produced by their efforts and the ongoing importance of these historical maps in current boundary administration. Paula Rebert explores how, despite the efforts of both commissions to draw neutral, scientific maps, the actual maps that resulted from their efforts reflected the differing goals and outlooks of the two countries. She also traces how the differences between the U.S. and Mexican maps have had important consequences for the history of the boundary.
- List of Illustrations
- Index Maps
- Chapter 1: On the Line: Field Surveys
- Chapter 2: The Boundary Office: Mapmaking
- Chapter 3: Consultation between the Commissions: Surveys on the Pacific and Gulf Coasts and the Colorado River
- Chapter 4: Cooperation in Surveying and Mapping: The Land Boundary
- Chapter 5: Controversy on the Boundary: Surveys of the Rio Grande
- Chapter 6: Authoritative Maps and the True Line
- Appendix: Map Authorities
Boundaries, when definite, are always marked upon the earth's surface by natural features, such as mountains or streams, or else by specific lines or curves; such boundaries when projected upon a map are easily understood.
—Astronomer Amiel W. Whipple to U.S. Commissioner John R. Bartlett,12 December 1850
The making of the boundary between the United States and Mexico was a matter of maps. Before the boundary existed on the land, treaty negotiators traced out the line on maps. They planned for surveyors, guided by the treaty maps, to fix the boundary on the ground and to demonstrate the results in authoritative maps. U.S. and Mexican surveys of the remote frontier and the maps created from them brought the boundary into being. The boundary maps made from the first surveys later became important in the evolution of boundary relations and defined the United States-Mexico boundary in a manner unexpected at the time of their making.
The boundary had its painful beginning in the U.S.-Mexican War, which was brought to an end with the Treaty of Peace, Friendship, Limits, and Settlement, signed at Guadalupe Hidalgo, 2 February 1848. At the treaty conferences, two of the four main stages in the process of boundary making were fulfilled. The first stage, the allocation of territory, was a matter of political negotiation and resulted in Mexico's cession of the states of Alta California, Nuevo México, and the northern portions of Tamaulipas, Coahuila, and Sonora—territory that would become the U.S. states of California, Nevada, Utah, Texas, and parts of Colorado, Arizona, and New Mexico. The cession opened up a vast new domain to the United States, while for Mexico, it was a grievous loss of half its territory. The second step, delimitation of the boundary—the choice of its location and its definition in written terms—was realized in the treaty itself. The new boundary superseded the dividing line between the territories of Mexico and the United States that had originally been defined in treaties between Spain and the United States. The third stage of boundary making, demarcation, was assigned by the treatywriters to government commissions that would locate and mark the boundary on the ground. Because the treaty delimitation could not define the line as exactly as surveyors would place it, the commissions would make fine decisions regarding the location of the boundary.
The writers of the Treaty of Guadalupe Hidalgo devised boundaries that followed both geometrical lines and rivers. Geometrical boundaries were frequently employed by diplomats who, lacking accurate geographic knowledge of the territory through which a boundary was to run, ruled a line upon a map. The ruled line was likely to conflict with the shape of the terrain, making access diffficult for surveyors and demanding complex surveys to establish a flat map line on the curving earth. Rivers also were often chosen as boundaries because they were conspicuous features on maps of little-known territories. A number of different lines following the banks or channels could be interpreted as a river boundary, however, and each presented different problems in surveying. In addition, river instability was likely to produce problems in the fourth stage of boundary making, maintenance, and administration. The lines the treaty writers chose afforded solutions for their deficient knowledge of the new United States-Mexico borderlands, but they were replete with possibilities for uncertainty and controversy.
The Treaty of Guadalupe Hidalgo described the boundary as it would run from east to west. The dividing line began offshore, as the delimitation explained: "The Boundary line between the two Republics shall commence in the Gulf of Mexico, three leagues from land, opposite the mouth of the Rio Grande, otherwise called Rio Bravo del Norte, or opposite the mouth of it's [sic] deepest branch, if it should have more than one branch emptying directly into the sea." At the time of the treaty, as now, the offshore waters or marginal sea were considered to be part of the national territory of a coastal nation; but the extent of the marginal sea has often been a matter of negotiation and has varied considerably with different nations at different times. In the nineteenth century, the extent of the marginal sea was generally accepted as three nautical miles, equivalent to one marine league, distant from the low-water mark on the coast. Both the United States and Mexico supported the three-mile doctrine, but the Treaty of Guadalupe Hidalgo specified, nevertheless, a boundary of three leagues, or nine miles, into the Gulf of Mexico. The provision was derived from an earlier act of the Republic of Texas.
By designating the river's deepest channel as the boundary, the treaty writers forestalled the possibility of contention in case the Rio Grande were discovered to have more than one outlet into the Gulf. Positioned, then, opposite the deepest branch of the Rio Grande, the boundary continued, "from thence, up the middle of that river, following the deepest channel, where it has more than one to the point where it strikes the Southern boundary of New Mexico." The treaty line followed the Rio Grande, the "Great River," known in Mexico as the Río Bravo (Great or Wild River) or the Río del Norte (River of the North). It was implemented as the boundary as a matter of political necessity, since a U.S. claim to the Rio Grande as the boundary of Texas had been a precipitating cause of the U.S.-Mexican War. The Rio Grande had not yet been fully explored when the treaty negotiators found it prominently, although inaccurately, represented on the map they used in their discussions, the Mapa de los Estados Unidos de Méjico (Map of the United States of Mexico) by John Disturnell (fig. I-1).
From the delimitation given in the Treaty of Guadalupe Hidalgo, two different lines in the Rio Grande could be understood as the boundary. The treaty used the words, "up the middle of that river," an expression that appeared to refer to the median line, a line everywhere equidistant from the nearest points on the opposite banks of the river; but the treaty also said, "following the deepest channel," designating a particular line in the river that depended upon depth soundings. In general, a median line marks the boundary in rivers that are not used for navigation, while navigable rivers are usually divided along the main channel, allowing access to the river by vessels of both nations—a concept known as "the principle of thalweg." Since the delimitation was ambiguous, its meaning had to be deduced from other statements in the treaty. Because another article guaranteed the right of navigation on the river, the contradictory language was usually construed in favor of the deepest channel, a construction that was complicated by the fact that much of the Rio Grande was not truly navigable.
The end of the Rio Grande boundary, where the southern boundary of New Mexico struck the river, was also shown on Disturnell's map. The treaty line then ran along generally straight lines, connecting several "turning points," positions assumed to be correctly known and precisely located. It followed the southern boundary of New Mexico to its western termination, then turned northward until it intersected the southernmost branch of the Gila River. In the words of the treaty, the line was to continue from the Rio Grande,
thence, westwardly along the whole Southern Boundary of New Mexico (which runs north of the town called Paso) to it's [sic] western termination; thence, northward, along the western line of New Mexico, until it intersects the first branch of the river Gila; (or if it should not intersect any branch of that river, then, to the point on the said line nearest to such branch, and thence in a direct line to the same;) thence down the middle of the said branch and of the said river, until it empties into the Rio Colorado; thence, across the Rio Colorado, following the division line between Upper and Lower California, to the Pacific Ocean.
The "town called Paso" was located where Cindad Juárez now stands and was also called E1 Paso or Paso del Norte after the nearby mountain pass of the same name. It was the important center of settlement in the area, as the Texas city of E1 Paso had not yet been established.
In order to clarify the delimitation, the treaty writers referred to Disturnell's map to illustrate their language and made the map a part of the treaty. The delimitation continued:
The southern and western limits of New Mexico, mentioned in this Article, are those laid down in the Map, entitled "Map of the United Mexican States, as organized and defined by various acts of the Congress of said Republic, and constructed according to the best authorities. Revised edition. Published at New York in 1847 by J. Disturnell:" Of which Map a Copy is added to this Treaty, bearing the signatures and seals of the Undersigned Plenipotentiaries.
The treaty writers reconciled their language with the representation in Disturnell's map, but they did not confirm that the map image agreed with geographical reality. In fact, the map contained a number of serious errors, particularly in its depiction of the Rio Grande and the town of Paso, important features named in the written delimitation of the boundary. In spite of its recent publication date, Disturnell's map was based on old information. It was copied with few changes from A Map of North America, published by Henry S. Tanner of Philadelphia in 1822. The depiction of northern Mexico in Tanner's map had depended upon several sources, including Alexander von Humboldt, Pedro Walker, Zebulon Pike, and William Darby, all authorities dating from about the first decade of the nineteenth century. Although these authorities had not yet been superseded in 1846, when Disturnell took over the map, the age of the sources demonstrated the lack of up-to-date information about the geography of northern Mexico that existed at midcentury. Disturnell, who was not a cartographer himself but rather a businessman who published directories, guidebooks, and maps, brought out the Mapa de los Estados Unidos de Méjico in response to public interest generated by the U.S.-Mexican War. In 1847, the year that treaty negotiations began, Disturnell published seven different printings of the map, each with additions and changes, which he termed "editions."
A copy of the seventh edition of Disturnell's map was carried to Mexico City for use in the negotiations by Nicholas P. Trist, the U.S. treaty commissioner. Trist did not think highly of Disturnell's map; he considered that it was "suddenly got up, as the mere speculation of an engraver or bookseller, to meet the demand in our country for Maps of Mexico." Trist and the Mexican treaty commissioners searched for more reliable geographic information than that provided by Disturnell's map but were unable to find a satisfactory authority. When diplomacy was concluded, the map that Trist had carried with him was attached to the U.S. copy of the Treaty of Guadalupe Hidalgo. The map that was attached to Mexico's copy of the treaty was the twelfth edition, also published in 1847. It is not likely that the negotiators realized that they had placed two different editions of Disturnell's map with the treaty, but the differences between the two editions apparently caused no complications in the boundary survey.
The errors present in both official editions of Disturnell's map, however, precipitated controversy. In relation to the graticule of the map, the Rio Grande was placed farther to the east than its true position, and the town of Paso was located too far north on the Rio Grande. Paso was actually located about two degrees farther west and thirty minutes farther south than shown on Disturnell's map. In addition, the displacement of the Rio Grande on Disturnell's map made the southern boundary of New Mexico appear to be about three degrees long, whereas the southern boundary actually reached about one degree west of the Rio Grande. The southern boundary of New Mexico was shown as though it were an established entity, when in fact it had never been demarcated. The U.S. Boundary Commission and the Comisión de Límites Mexicana (Mexican Boundary Commission) appointed under the Treaty of Guadalupe Hidalgo discovered the problems in Disturnell's map when they arrived at Paso in December 1850, although the errors had been suspected well before then.
The map's discrepancies raised doubts about the correct location of the boundary line west of the Rio Grande. Because Disturnell's map was an integral part of the Treaty of Guadalupe Hidalgo, U.S. Boundary Commissioner John Russell Bartlett and Mexican Boundary Commissioner Pedro García Conde had to decide whether the line should be determined by the latitude shown on the map or by its position relative to the town of Paso, as shown on the map. After extensive discussions, the commissioners directed an engineer from the Mexican commission, José Salazar, and an engineer from the U.S. commission, Amiel Whipple, to examine Disturnell's map, make measurements on the map, and prepare a written report. The engineers' findings served as the basis for an agreement between the commissioners that became known as the Bartlett-García Conde compromise. Salazar and Whipple reported as follows:
With a certified copy of the Treaty Map before us, we proceeded to make a scale of minutes of latitude, by dividing into 120 equal parts, the length of that portion of a meridian laid down upon the Map between the parallels of 32° + 34° of North latitude.
In a similar manner we found a scale of minutes of longitude for that degree of latitude, which passes through points of the Southern Boundary Line of New Mexico as indicated upon the same Map.
Then, measuring the distance from the point where the middle of the Rio Grande strikes the Southern Boundary of New Mexico, South to the parallel of latitude marked 32°, and applying it to our scale of minutes of latitude, we found the length equal to 22' of arc. This reduced by Francoeur's tables is equal to 40659 metres = 25 1/4 english miles = 21.92 Geographical miles.
Finally, taking the distance from the point aforesaid to the extreme Western limit of the Southern Boundary of New Mexico, and applying this distance to our scale of minutes of arc in longitude, we found it to be 3°; which in this latitude, according to tables of Francoeur is equal to 282220.2 metres = 175.28 English miles = 154.14 Geographical miles.
Therefore, according to this determination, the point where the middle of the Rio Grande strikes the Southern Boundary of New Mexico, is 22' of arc North of the parallel of latitude marked 32° upon the Map. From the same point thence the Southern Boundary of New Mexico extends 3° to its Western termination.
The commissioners upheld the engineers' verdict that the boundary should run along the 32°22' parallel, further north than its position on Disturnell's map relative to the town of Paso, for three degrees west from the Rio Grande, as shown on the map (see Location Map 3). The Bartlett-García Conde compromise gave the United States more territory to the west than the true southern boundary of New Mexico would have enclosed and gave Mexico more territory to the north than the true position of Paso would have allowed. The commissions proceeded to establish the initial point of the boundary on the 32°22' parallel at the Rio Grande, near the town of Doña Ana; and the Mexican commission, satisfied with the Bartlett-García Conde agreement, continued to survey the entire southern boundary of New Mexico. Discontent with the newly established initial point began to disrupt the U.S. commission, however, as some commission members argued that the initial point had been located much farther north than intended by the Treaty of Guadalupe Hidalgo. The controversy grew until many people were drawn into it, including residents of the border area and the governments of New Mexico and Chihuahua. Public opinion in the United States increasingly found the Bartlett-García Conde compromise unacceptable and demanded renegotiation of the boundary delimitation. Meanwhile, U.S. survey operations stagnated, until at length Congress suspended appropriations, and the boundary commission was recalled.
Before the survey collapsed, the U.S. and Mexican commissions completed the Gila River survey and the California line. The boundary followed the middle of the Gila River to its confluence with the Colorado River, crossed the Colorado, and struck a straight line to a point one marine league due south of the southernmost point of the port of San Diego. The dividing line between Alta California, allocated to the United States, and Baja California, still a Mexican possession, had been strongly debated in the negotiation of the Treaty of Guadalupe Hidalgo. The Mexican diplomats had specific instructions not to relinquish the port of San Diego, while for the U.S. commissioner, the acquisition of San Diego was a fundamental goal. Mexico ultimately surrendered San Diego because the town had been perceived as part of Alta California since the time of its founding, but the boundary between the Californias was particularly carefully defined in the treaty.
Another map was consulted to support the delimitation of the California line. "In order to preclude all difficulty in tracing upon the ground the limit separating Upper from Lower California," the treaty stated,
it is agreed that the said limit shall consist of a straight line, drawn from the middle of the Rio Gila, where it unites with the Colorado, to a point on the Coast of the Pacific Ocean, distant one marine league due south of the southernmost point of the Port of San Diego, according to the plan of said port, made in the year 1782, by Don Juan Pantoja, second sailing-Master of the Spanish fleet, and published at Madrid in the year 1802, in the Atlas to the voyage of the schooners Sutil and Mexicana: of which plan a Copy is hereunto added, signed and sealed by the respective Plenipotentiaries.
Duplicates of the plan of the port of San Diego were attached to the U.S. and Mexican copies of the treaty (fig. I-2). The duplicates were tracings made from the Spanish atlas named in the treaty, drawn at Mexico City while the treaty was being negotiated; the Mexican tracing was signed by Romualdo Rivera and the U.S. tracing was made or directed by Captain Robert E. Lee of the U.S. Army. The boundary line was added to the tracings of the Pantoja map. Labeled "Boundary Line Linea Divisoria," it ran just below Punto de Arena, on the coast south of the bay. No designations of latitude or longitude were given anywhere on the tracing of Pantoja's plan, so that the boundary between the Californias was delimited in relationship to the topography, the features of the land surface.
The impasse that resulted from U.S. rejection ofthe Bartlett-García Conde compromise was resolved only through settlement of a new boundary treaty. While treaty negotiations were under way, U.S. and Mexican Boundary Commissions returned to the field and completed the survey of the Rio Grande. On 30 December 1853, the treaty commissioners in Mexico City signed a new treaty, and after extended debate in the U.S. Congress, ratifications were exchanged on 30 June 1854. Referred to by the participating diplomats as the treaty "of clarification of the Treaty of Guadalupe," the Treaty of 1853 nullified or revised several articles of the earlier treaty and provided a new boundary delimitation. It replaced the southern boundary of New Mexico as shown on Disturnell's map and the line in the Gila River with a boundary south of the Gila that followed specified geometrical lines connecting several new turning points, and a short jog along the Colorado River. As part of the treaty, the United States purchased from Mexico the territory between the Gila River and the new boundary. In the United States, the treaty became known as the Gadsden Treaty or the Gadsden Purchase after its U.S. negotiator; in Mexico it was called the Tratado de la Mesilla, named for the principal area in controversy, the Mesilla Valley, that was settled by the treaty. Both nations used the more neutral name, Treaty of 1853.
The new treaty noted that the dividing line between the Californias would remain as already defined and established and repeated the delimitation of the Rio Grande boundary that had been given in the 1848 treaty. The Treaty of 1853 specified the limits in the Rio Grande as follows: "Beginning in the Gulf of Mexico, three leagues from land, opposite the mouth of the Rio Grande as provided in the fifth article of the Treaty of Guadalupe Hidalgo, thence as defined in the said article, up the middle of that river." The new portion of the boundary was to begin at
the point where the parallel of 31°47' north latitude crosses the same [Rio Grande], thence due west one hundred miles, thence south to the parallel of 31°20' north latitude, thence along the said parallel of 31°20' to the 111th meridian of longitude west of Greenwich, thence in a straight line to a point on the Colorado river twenty English miles below the junction of the Gila and Colorado rivers, thence up the middle of the said river Colorado until it intersects the present line between the United States and Mexico.
Thus the new delimitation retained much of the boundary that had already been surveyed while it required new surveys in order to connect the Rio Grande boundary and the California line.
Shortly after ratification of the Treaty of 1853, the U.S. and Mexican Boundary Commissions renewed their surveying operations, completing the fieldwork in 1855. The surveys established a boundary 1,952 miles (3,141 km) long, excluding maritime boundaries, from the Gulf of Mexico to the Pacific Ocean: 1,254 miles (2,019 km) on the Rio Grande; 533 miles (858 km) from the Rio Grande to the Colorado River; 24 miles (38 km) on the Colorado River; and 141 miles (226 km) from the Colorado River to the Pacific Ocean. The work of the boundary commissions was not over, however, for with the boundary surveyed and marked in the field, the second of its two distinct but interdependent projects remained to be completed: that of compiling and producing authoritative maps of the line surveyed and marked. The final boundary maps were completed two years later, in 1857, with the U.S. commission and the Mexican commission each depositing a set of maps with their respective governments, to be held as legal records of the boundary.
The maps contributed at once to the nineteenth century's expanding geographical knowledge of the world. The region that had become the borderlands through settlement of the U.S.-Mexican War was little known, and the maps produced by the boundary commissions were the first to portray the extensive area from an organized, scientific survey. In the surveying and mapping operations of the joint commission, as well as in the scientific investigations carried out in conjunction with the survey, the work was conceived by its practitioners as a contribution to world scientific knowledge. A U.S. scientist who traveled to Europe while the survey was in progress, carrying with him copies of some of the early boundary maps completed by the U.S. commission, wrote to the commissioner to describe their European reception: "And how are you coming on with your maps?" he asked; "The four first of which you gave me copies to take along and distribute in Europe have created general attention among men of science[,] geographers especially, both as works of art, as on account of their intrinsic value for the knowledge of that part of the globe[']s surface. I have left copies with the Geographical Societies of Berlin, Frankfort and other places and with Baron Von Humboldt, who expressed himself as being familiar with your name and as highly pleased with the whole work." Historians later recognized the high achievement that the boundary surveys represented. William Goetzmann named the boundary survey as "one of the best of the surveys" of the U.S. Corps of Topographical Engineers, and Manuel Orozco y Berra marked the boundary survey as one of the best works carried out by the Mexican engineers.
The results of the boundary surveys were incorporated into national maps of Mexico and the United States. In Mexico political turmoil had prevented orderly surveying and mapping of the new nation in the years following independence in 1821. The Sociedad Mexicana de Geografía y Estadística (Mexican Society of Geography and Statistics), at its founding in 1833, organized a project to produce a general map of the nation, but the map was not completed until 1850. Compiled from many sources, and including the northern territories that had been lost to the United States, Mexico's most authoritative national map was already outdated at the time of the boundary survey. With the survey's conclusion, efforts to map the national domain were renewed. An atlas that presented a national map and maps of the Mexican states with geographical and statistical information, compiled by engineer, geographer, and writer Antonio García y Cubas and supported by the Ministerio de Fomento (Department of Development), was published in 1858, a year after the boundary maps were completed. The atlas's long list of map authorities—persons who had gathered the survey data on which the maps were based or who had contributed to their making—included members of both the Mexican and U.S. Boundary Commissions.
In the United States, survey results contributed to two important maps of the western states and territories. The U.S. Boundary Commission prepared a general map of the Transmississippi West, one of the first to present an overall view of the West as a compilation of U.S. government surveys, that was published with the commission's final Report in 1857-58. The officer who had charge of the map's printing noted that "The map now is considered one of the best maps ever published and great demands are made daily for copies of it." It did not long retain its standing as the master map of the Transmississippi West, however, for even as it was being prepared, another map was being raced to publication. Topographical Engineer Gouverneur Warren, working in the Office of Pacific Railroad Surveys, produced a map of the West nearly simultaneously with that of the boundary commission. Drawn at a larger scale than the boundary commission's map, Warren's map was compiled by comparing and analyzing the data from a large number of surveys and included an image of the new U.S. borderlands based on boundary survey information. Some historians have judged Warren's map of the West to be a landmark map, the culmination of six decades of exploration and mapping.
Some forty years after the original survey, the geometric boundaries were resurveyed by U.S. and Mexican engineers. The original demarcation had been made with only a few, widely spaced monuments, many of which were destroyed in time, so that the boundary was poorly marked. Because of disputes over the exact location of the boundary that arose as adjacent lands became more settled, the United States and Mexico agreed to restore the boundary monuments and erect new ones to mark the line where it ran overland. An International Boundary Commission performed the resurvey in the years 1891 to 1896 and prepared a new set of maps of the land boundary. The plan of operations drawn up between U.S. and Mexican engineers was based on relocating the original monuments; the terms of their agreement stated that "al1 monuments whose position, after verification, are found to be as located by the International Boundary Commission of 1849-56 shall be accepted as positive boundary marks." The maps of the original survey were crucial in recovering the monuments on the land and in verifying that the markers found were in fact those erected in 1849-56.
The maps of the original survey also aided in maintaining the boundary in the Colorado River and the Rio Grande. An International Boundary Commission to resolve problems relating to the river boundaries was first created in a treaty between the United States and Mexico in 1889. The commission was to investigate changes that had occurred in the course of the Rio Grande and, in each case, decide upon sovereignty of the adjoining lands. Locating the old bed of the river and ascertaining the extent and location of change was often assisted by reference to the maps of the original survey. The maps were also called upon as evidence in international hearings to resolve boundary questions. The role of the maps in providing evidence became most important when judicial concern fell upon the boundary maps' authority and the permanence of the Rio Grande boundary.
Another concern, the management of water resources, became increasingly important as population in the borderlands grew, and several new treaties clarified water management and boundary issues. The Treaty of 1944 made extensive provisions for the utilization of the waters of the Rio Grande, Colorado, and Tijuana Rivers and renamed the boundary commission as the International Boundary and Water Commission (Comisión Internacional de Límites y Aguas), charging it with carrying out the terms of the treaty. In 1970 the Treaty to Resolve Pending Boundary Differences and Maintain the Rio Grande and the Colorado River as the International Boundary continued the commission's jurisdiction over boundary matters. Mapping requirements spelled out in the Treaty of 1970 maintain surveying and mapping among the commission's important activities. The International Boundary and Water Commission coordinates mapping projects with U.S. and Mexican national mapping agencies, embracing cooperation on many cartographic issues, such as the exchange of data, map materials, and information on mapping programs, shared geodetic control along the border, publication of cartographic information furnished by the other country, and acquisition and distribution of aerial photography.
The example for cooperation in boundary work by specialists from both the United States and Mexico was set in the original surveying and mapping project of 1849-57. The participation by representatives of both nations in the surveys and the reflection of their proceedings in the final maps are important themes for boundary history. The decisions and agreements of the original U.S. and Mexican Boundary Commissions became the foundation for future boundary relations, initiating open and professional negotiations for boundary administration. The maps they produced, on the other hand, became significant because each commission maintained independence in its surveying and mapping operations. The existence of two sets of official boundary maps, one made by the United States and one by Mexico, would later have consequences for the development of boundary relations between the United States and Mexico; but these consequences were not revealed until half a century after the original survey was completed. The making of maps by the U.S. and Mexican commissions set the course of boundary history.