OCR Text |
Show 83 position of this point has been accurately determined; and then proceeded to the head of the west branch of the south fork of the Rio Grande and made a topographical station upon a high and sharp peak seven miles east of Mount Macomb. Snow nad meanwhile fallen to the depth of from 10 inches to 1 foot upon the mountains, rendering mountain- work very disagreeable, and oftentimes dangerous, from slipping. On November 2, we were compelled thereby to bring our work in the high mountains to a close, after four and a half months of continuous and almost excessive labor in the high masses forming the Atlantic and Pacific divide and its outlying spurs. From Del Norte the road via the Mosca Pass was meandered, the Huerfano traced to its mouth, and the Arkansas meandered thence to West Las Animas, where I disbanded the three parties of the Colorado section about the 25th day of November, 1875. During the field- season the system prescribed by the printed instructions issued from the office of the survey in 1874 was carried out. Nineteen triangulation- stations were occupied oy Mr. Spiller and myself, the principal of which were selected for their well-defined and sharp peaks as well as on account of their position in the scheme of triangles. The principal angles were repeated from six to twelve times. As soon as a peak was occupied, a substantial stone monument was built to a height of from 6 to 14 feet, and these monuments taken as targets thereafter. Prior, however, to the occupation of peaks, the natural object itself was taken as the target. In most oases, however, these points were very sharp and well- defined, so that monuments were scarcely necessary. The angles were read from a 6- inch WUrdemann theodolite, graduated to read to 10 inches, the stations being from 15 to 60 miles apart. Where practicable the sides were near 30 miles in length, but in carrying the triangles across the wide stretches of mesa- country in the San Juan basin, where but few well- defined points were visible, long sights were necessary. Probably the largest triangle which has ever been measured falls in Colorado and New Mexico, viz: La Plata Creek; Banded Peak; Mount Taylor. Miles. From La Plata to Banded it is 83.905 From Banded to Mount Taylor 139.876 From La Plata Peak to Mount Taylor 154.499 From Gray's Peakt near Denver, to Mount Taylor, the azimuth is carried by four lines of sight: Miles. 1. Gray's Peak to Hunt's Peak 86.250 2. Hunt's to Uncompabgre 71.515 3. Uncompahgre to La Plata Peak 55.200 4. La Plata to Mount Taylor 154.499 Total 367.464 Also, Miles. 1. Gray's Peak to Pike's Peak 65.614 2. Pike's to Sierra Blanca 90.338 3. Sierra Blanca to Banded ; 70.791 4. Banded to Mount Taylor 139.876 • Total 366.619 The first line of sights was carried by ray parties, Mr. Nell and Mr. Spiller measuring the angles, from Gray's Peak to Mount Taylor; the second, as far as to the Sierra Blanca. Banded Peak was occupied by Lieutenant Morrison's party in 1875 and Mount Taylor by Lieutenant Price's party in 1874, and re- occupied the past season by Lieutenant Morrison's party, the angles being read by Messrs. Thompson and Clarke. Sierra Blanca was re- occupied 1875 by Mr. Maxson, of Lieutenant Carpenter's party. In addition to the triangulation- stations, which have all been computed, seventy- seven high peaks were occupied as topographical and secondary triangulation- stations. Upon these the angles were read to the nearest minute, repeated to primary stations to give sufficient reliable data for the computation of the position of the more important of these points. Seventy- four lower points were also occupied, which were mathematically fixed, and numerous check- stations introduced upon the meander- lines. Upon each tdangulation and topographical station a panoramic view of the horizon was made in perspective and sights taken to all points not too distant, such as peaks, ends of marked spurs, junction- courses, and bendB of streams, towns, ranches, and other artificial features; and these points accurately located in relative horizontal position by intersections, and vertically by angles of elevation or depression. In the immediate neighborhood of the stations horizontal plans showing the local topographical details |