GEODETIC AND TOPOGRAPHICAL.

Measured and developed bases were laid out at Los Angeles, Weldon, and Panamint Valley, in the California section. None were found necessary or requisite in the Colorado section.

The sketch herewith shows the progress made in the development and number of the secondary triangulation belts in the Colorado section, and will at an early day be supplemented by a map showing the devel opment of triangles from the Los Angeles base to the eastward. Triangulation observations have been made by each one of the moving field-parties over large areas in California, Nevada, Colorado, and New Mexico.

A list of geographical positions, other than those given in the pres ent report, will appear in the list of astronomical positions in Volume II; other positions in the appendix of part second, Volume II, giving alti tudes of prominent positions, and the remainder in Volume I of the sur vey publications.

The areas in Colorado, New Mexico, California, Nevada, and Arizona were occupied in accordance with the project submitted to and approved by the Chief of Engineers and Secretary of War.

Many connections have been made with the stakes and other marks of the public-land surveys. The degree of progress in topographical accuracy of delineation is one of the notable features of the year. The outgrowth from the surveys of the parties under Lieutenant Marshall admitted of the construction of a special sheet of the San Juan mining region, on a scale of 1 inch to 2 miles, being an independent map of onefourth the area of the southwest quarter of atlas-sheet 61, which area has also been reproduced and published, on a scale of 1 inch to 4 miles, during the year. The mountainous portions of the country having in tricate drainage areas are now all delineated and published, upon a scale of 1 inch to 4 miles, while plateau and semi-desert areas are drawn upo a scale of 1 inch to 8 miles. The larger scales are also susceptible of reduction to the uniform scale proposed for the atlas of the entire see tion west of the one-hundredth meridian. Many monuments have been built, and the positions occupied are susceptible of identification and further use in connection with a extended scheme of triangulation, or for the purpose of fixing accurately the positions of minor points that may spring into importance in succeeding years.

ROUTES OF COMMUNICATION.

Tables of distances and road-profiles have been computed over the principal traveled routes and important trails in those portions of Colorado and New Mexico, Southern Califorinia, Utah, and Arizona over which the surveys have extended. These are based upon odometer and barometer measurements of the survey. In addition to the simple distances, the facilities for camping are noted.

Such tables, together with material gathered in the field-season of 1876, will furnish the basis of an extended set of tables, and supply to a great extent a need long felt for authoritative distances over a country where the distribution of water is such that the traveler needs to know where he may find wood, water, and grass or grain to guide him in his selection of routes and camps. These tables, with profiles of the more important routes, it is proposed to publish in separate form at an early day, as stated in report of last year.