Each division was accompanied by a small escort. These escorts were (with the exception of one corporal and six men, with Lieutenant Hoxie, detailed from the military department of the Platte, General E. O. C. Ord commanding) drawn from the military department of the Missouri, General John Pope commanding, the larger portion of the latter having been detailed from the military district of New Mexico, Col. J. Irwin Gregg commanding. These escorts were distributed among the several working field-parties, and were in numbers sufficient only for the protection of the lives of the members of the expedition and for guarding the public property. The necessary number of guides, packers, herders, laborers, &c., accompanied the expedition.

The Denver division, or Colorado party, under Lieut. W. L. Marshall, Corps of Engineers, was occupied for the entire season in Colorado, and completed most successfully the duties assigned to it in that field. Executive reports submitted by Lieutenants Hoxie and Marshall are herewith.

Report of Lieut. R. L. Hoxie, Corps of Engineers.

UNITED STATES ENGINEER OFFICE,
GEOGRAPHICAL EXPLORATIONS AND SURVEYS

WEST OF ONE HUNDREDTH MERIDIAN,
Washington, D. C., January 1, 1874.

SIR: I have the honor to submit the following executive report of operations under my charge during the field season of 1873:

The party to which I was assigned as executive officer in charge was organized at Salt Lake City, Utah, and consisted of Gilbert Thompson, topographer; Edwin E. Howell, geologist; William Somers, meteorologist; Alexander Brown, odometer recorder; one cook, one cargadore, and four packers, with an escort of one sergeant and five privates from the military Post of Beaver, Utah.

The party left Salt Lake City on May 30th, and operated, until September 7th, east of the Wahsatch Mountains, in Castle Valley, working its way southward to the Colorado River, over the western part of Castle Valley, the portion of country required to complete atlas sheets Nos. 50, 59, and 67, at that time preparing for publication.

On the 7th of September we crossed the Colorado River and proceeded by way of Oraybe and the Moquis Pueblos to Fort Wingate, N. Mex., whence, after refitting, we proceeded southward, co-operating with the other parties in New Mexico and Arizona Territories, and, returning at the close of the season, disbanded at Fort Wingate on the 25th of November.

During the three months' operations in Utah about fifteen hundred topographical and triangulation stations were occupied, and one thousand and twenty-five miles of meander lines measured, besides which numerous detours were made for the ascent of prominent points as triangulation stations. The latitude and departure of camp was computed each night, the meander lines of the day plotted, and the principal topographical features drawn upon the field-map. Sextant observatious for latitude upon north and south stars, and observations on Polaris for maguetic declination, were taken at each camp. The meridian of Provo was connected with that of the observatory at Salt Lake City, time-signals having been sent over the wires of the Deseret Company, freely tendered to the expedition by the courteous action of D. Milton Musser, superintendent.

The cistern and aneroid barometers, with the psychrometer, were read at regular intervals in camp and at all points that would serve to indicate the reliet of the country.

About six thousand square miles of a very difficult mountain and cañon country was mapped here.

The accuracy of the work depends upon the triangulation and the latitude-checks. The former was entirely upon natural objects, the peaks of the Wahsatch range, the Henry Mountains, Navajo, and prominent mesas, and made with the gradienta by Mr. Thompson, who has shown more than ordinary skill and energy in performing rapid and accurate work. We derived much assistance from Mr. Howell, whose investigations in geology were necessarily carried on in intimate connection with the topography.

The sextant observations were made entirely by myself, and the aver age probable error of the results is about ten seconds of arc.

More time was taken in this part of our field of operations than allowed by your instructions, but this was necessitated by the obstacles encountered. In the month of June we found the high passes of the Wahsatch Range blockaded with snow and mud, and the streams on the eastern slope were swift, cold, and deep, causing serious detentions. Later in the season we had worked our way southward into the cañon country, in which progress was necessarily slow, and a scarcity of grass and water added to the difficulty of traversing the country. At this time two of my packers deserted with thirty-two mules, and caused a further delay of about twenty days. The time was usefully employed, however. The full working force kept the field as usual, and although I had not intended to give the time here, the work done in consequence could not well have been dispensed with. The recovery of the mules, with the men who ran them off, cost me a chase of four hundred miles, the return being accomplished in two hundred more, over the wildest part of a difficult country.

We encountered considerable hardship during this part of our season's work, being frequently without good water, and sometimes without any. At one time we subsisted for seven days upon hard corn, brought along for the mules, and taken from them when they could ill spare it.

It was not possible to sacrifice close work to the pressure of time, as the devious track which covered so much ground was forced upon us by the difficult nature of the country.

A portion of the results of this part of the season's work are already published in Atlas sheets Nos. 50 and 59, and Mr. Howell will report upon the geology and mineralogy of the country so far as observed by him.

From the crossing of the Colorado to Fort Wingate, the most direct route was taken and no attempt was made to map the country through which we passed. The trail was carefully meandered, however, the topography adjacent sketched in, and frequent bearings taken as checks upon prominent points, with the usual latitude-checks for the camps and the observations with cistern barometer, aneroid, and psychrometer. The primiary object here was celerity of motion, the survey recommencing at Fort Wingate. The length of measured meander line was about two hundred miles.

Soon after leaving Fort Wingate Mr. Thompson was detached by your order, with a small party, to carry a system of triangles over the ground covered by my own and the other parties then operating together in New Mexico. This work was successfully accomplished. Base lines

were measured at Fort Tulerosa and Fort Bayard, and others located to be measured next season.

The work of my own party in this section of the country was conducted in the same manner as in Castle Valley during the earlier part of the season; but, having much more favorable conditions, better results were obtained.

About five thousand square miles were covered along the Atlantic and Pacific divide, in the section of country embraced in Atlas sheets Nos. 76, 83, 77, and 84.

This has been mapped and is ready to be transferred to the Atlas sheets.

Detailed reports of the geology and mineralogy of the region traversed will be submitted by Mr. Howell and Dr. Oscar Loew.

Very respectfully, your obedient servant,

Lieut. GEO. M. WHEELER,

Corps of Engineers, U. S. A.

R. L. HOXIE,

Lieut. of Engineers, U. S. A.

Report of Lieut. W. L. Marshall, Corps of Engineers.

UNITED STATES ENGINEER OFFICE, GEOGRAPHICAL EXPLORATIONS AND SURVEYS WEST OF THE ONE HUNDREDTH MERIDIAN, Washington, D. C., June 30, 1874.

SIR: I have the honor to submit the following executive report of the operations of the Colorado party of the expedition for explorations and surveys west of the one hundredth meridian, during the field season of 1873.

In accordance with the annual project, approved by the Secretary of War and Chief of Engineers, and pursuant to instructions from you, I organized the party at Denver, Colo., about June 1, 1873. Its personnel was as follows: First Lieut. W. L. Marshall, United States Engineers, executive officer and astronomer; Dr. J. T. Rothrock, acting assistant surgeon, United States Army, surgeon and naturalist; Prof. J. J. Stevenson, geologist; J. J. Young, topographer; Edgar Schroeder, assist ant topographer; Prof. John Wolf, collector in botany; Bernard Gilpin, meteorologist, and a small escort of enlisted men from the Fifth Infantry. Including packers and employés the party numbered forty-two men. Later in the season we were joined by Mr. Louis Nell, chief of triangulation. Pending the organization of the main party, on the 8th day of June a small topographical party was sent out to define the bases of the mountains, or "hogsbacks," from the mouth of the Platte Cañon to Golden City, with orders to join the main party at Georgetown, Colo., on the 16th.

On the 17th of June, having received at Georgetown the necessary supplies, I sent the main party, under Dr. Rothrock, to encamp near Fair Play, in South Park, to allow the collectors in natural history an opportunity to make full collections in the several branches in that vicinity, and to establish a meteorological station at the permanent camp. My small party retraced their course to Idaho Springs, visited the mines at Central City and Black Hawk; thence, by way of Chicago Lake and Mount Evans, to Georgetown, making the necessary topographical stations. On June 22 the Atlantic and Pacific divide was crossed

at the Argentine Pass, and from this date to July 4 the party worked about the heads of the Blue and Platte Rivers, in the cross range between Middle and South Parks, and in the Blue River range, making the ascent of Lincoln Peak and such other stations as were necessary to give a knowledge of the topography of this region.

Leaving the collecting party at Fair Play with orders to move camp to Twin Lakes, on the west side of the Upper Arkansas River, by August 1. the field party proceeded to survey the mountain-ridges bounding South Park, examined the country about the heads of the North Fork of the South Platte; the Kenosha range from Mount Evans to the Platte and Arkansas divide; this divide from the southeastern limit of South Park to the head of the South Fork of the South Platte River, meandering en route the principal roads and streams, and making the necessary stations upon mountain-peaks to check by triangulation the principal points of the survey. Wet Mountain Valley was visited, and the Arkansas River traced from near Cañon City to Granite C. H., at which place we arrived August 1, 1873.

During this interval, July 5 to August 1, Mr. Schroeder was employed with a small topographical party in collecting topographical data and in meandering roads and streams in South Park not traced upon the plats of the General Land-Office, and not visited by my own party.

From the non-arrival of supplies forwarded by the Quartermaster's Department from Cheyenne, a delay of several days was necessitated, which interval was spent in the immediate vicinity of Twin Lakes in collecting topographical details. A base was measured and an accurate trigonometric survey of the lakes made, and the topographical features relatively located from it. Two lines of soundings across either lake were made at the request of Prof. Stevenson.

On the 6th of August, having purchased the necessary supplies, the geologist and topographer were sent to visit the mines at Oro City, Colo., and McNutty gulches, and Homestrike Mountain, and to examine the country about Ten-Mile Creek, one of the tributaries of the Blue River; the western slope of the Blue River range; to meander Eagle River and its main branches, and to define the northern limit of the main or Saguache range west of the Arkansas River.

This party having accomplished its object, returned to the permanent camp at Twin Lakes on August 18. On the following day, still leaving the collecting party at Twin Lakes with facilities to extend the field of their investigation wheresoever they pleased, two topographical parties were dispatched-Mr. Schroeder, assistant topographer, to collect topographical data and meander the streams flowing into the Arkansas north of Lake Creek; to fix the water-shed and locate the heads of the middle branch of the Roaring Fork of the Grand River; while my own party crossed the divide at the head of Lake Creek, and from August 19th to September 3rd were engaged about the heads of the Gunnison River, and the southern tributaries of the Roaring Fork of the Grand River stations were made upon prominent peaks in the Elk Mountains, and also in the Saguache range at the beads of Chalk and Cottonwood Creeks, and the cañon of Taylor River traced to the junction of this stream with East River.

On the 3d of September the party was joined by Mr. Nell, chief of triangulation, from Fort Wingate, N. M.

On September 5th, he was sent with orders to make triangulationstations near the junction of the Eagle and Grand, at the northern extremity of the Saguache range, in the Blue River range, upon Gray's Peak and Mount Evaus, connecting the former with the astronomical

point at Georgetown; thence to proceed by the shortest road to Pike's Peak, which point had been located from a base measured near the astronomical station at Colorado Springs by Dr Kampf, making secondary stations en route; thence via the southern rim of South Park and the Platte and Arkansas divide to South Arkansas Creek, and thence to Fort Garland, making the necessary stations to give a connected system of triangles from the northern to the southern limit of our survey, from which points those occupied by Messrs. Young and Schroeder could be fixed. These orders were carried out by Mr. Nell, except that he was prevented by snow from actually occupying one of the main stations near the head of the South Arkansas, suggested to him. This point, though quite accurately fixed in longitude and latitude, must be occupied the coming season.

From September 5 to October 10 two parties were continuously employed in completing the survey of the drainage-areas of the upper Arkansas, and that part of the area drained by the Gunnison River which lies east of the one hundred and seventh meridian. From the 10th of October to November 4 a line-survey was run up the valley of the Rio Grande River to the San Juan mining district, but snow, which fell to the depth of 13 inches on the 15th, 16th, and 17th of October, prevented any further work in this region at high altitudes and effectually prevented any main stations on mountain-peaks. The Las Animas River was headed, and a line run down this stream connecting with Mr. Nell's trail from Fort Wingate, thence via the Pagosa Hot Springs, Tierra Amarilla, aud the head of the east branch of the Chama, and the San Antonio River to Fort Garland.

The streams tributary to the Rio Grande from the west and its main South Fork had meanwhile been meandered by a small party. The Sangre de Christo range south of Fort Garland as far as the New Mexiean line was also surveyed by Mr. Young. The interval from November 4 to November 14 was employed by Mr. Nell in measuring a base near Fort Garland and expanding it to his triangulation-stations.

A small party under the direction of Dr. Rothrock was dispatched on November 9 to Denver via Wet Mountain Valley, the Hardscrable Mines at Rosita, the Coal Mines at Cañon City, Colorado Springs, and mouth of Platte Cañou, to define the limits of the foot-hills and meander certain roads and streams. This party arrived at Denver December 4th, 1873. The measurement of the base and the local triangulation about Fort Garland having been completed, the escort returned to its station and the supernumerary employés were discharged. My party leit Fort Garland November 14, and proceeded, via the Aheyta Pass, to the east of the Sangre de Cristo range, headed the Cucharas, the Apishpa, the Purgatoire, and the North Fork of the Canadian River, made a triangu lation station upon the Greenhorn Mountain; then proceeded via Mace's Hole, Red Creek, Cañon City, Oil Creek, the Cañon of the South Platte, North Fork of the South Platte, and Turkey Creek, to Denver, making the necessary topographical stations en route, and, with the lines already run by Messrs. Nell and Young, completing the survey of the foot hills. On the 10th day of December the parties were disbanded at Denver, Colorado.

METHODS OF SURVEY.

The two peaks, Gray's and Pike's, were located from the astronomical stations at Georgetown aud Colorado Springs, C. T., and the computed length and azimuth of the line connecting them were used as a base for our triangulation.