The three surveying parties organized for field work in June, 1889, by Mr. Lyman Bridges were disposed as follows: The first, under the charge of Mr. Francis Bridges, assistant engineer, prosecuted the topographic survey of Independence reservoir site; the second party, under the charge of Mr. L. H. Shortt, assistant engineer, made preliminary surveys for canal lines from the lower Truckee River, in the neighborhood of Wadsworth; and the third party, in charge of Mr.

George A. Brown, assistant engineer, was engaged upon the topographic and engineering survey of the Hope Valley reservoir site, within the Carson River watershed.

In the following pages is given a brief description of the surveys which have been completed and for which the computations, maps, and estimates have been prepared. The statements of capacities of the reservoirs definitely surveyed and of the length and heights of dams are to be considered as preliminary merely, as in order to reach definite conclusions regarding the most feasible and economical sites it will be necessary to complete the hydrographic survey. Until this is done a knowledge of the quantities of water available for storage and of capacity and economy of construction can not be reached.

Tahoe Tunnel.-Lake Tahoe is the greatest natural lake basin of the Sierra Nevada range, and one of the largest lakes held within mountain walls at a high altitude on the American continent. Its maximum length is 22 miles and its greatest width 13 miles. Its area is about 195 square miles, and it is at an altitude of about 6,225 feet. Its greatest depth is said to be 1,500 feet. This lake has a tributary watershed of over 500 square miles (inclusive of its own surface), constituting the upper portion of the drainage basin of the Truckee, which river is its outlet channel.

Lying parallel to and east of the Tahoe Basin, and separated from it by an arm of the Sierra known as the Tahoe Range, is the main upper valley of the Carson River. The elevation of this plain varies between 4,600 and 4,850 feet above sea level, or is from 1,350 to 1,600 feet lower than the plane of Tahoe's water surface.

The Tahoe tunnel line survey was made for the purpose of testing the feasibility and estimating the cost of piercing the Tahoe Range by a tunnel through which to draw water from the lake for use in Carson and other valleys through which the Carson River runs.

By the contour work of the Topographic Section of the Geological Survey the range was found to be narrowest opposite the southeast quarter of the lake. To definitely determine

the best location here for a tunnel line two trial meander lines were run over the mountain from the lake to the contour 20 feet below the elevation of the lake's low-water plane, on the east face of the range. These lines determine the shortest direct distance through from Boundary Bay to Haines Creek Canyon to be 17,331 feet, or 759 feet less than from Zephyr Cove to Genoa Canyon. This difference in favor of the former route, together with other advantages as to outcome, led to its adoption for further examination. Accordingly, a direct line was run between the two first-named points, and by leveling a ground profile was made thereon. The following are the data for these lines:

The Boundary Bay line commenced at a point on the shore of Lake Tahoe in the cove known as Boundary Bay, at the mouth of Small's Creek, and 3,169 feet north of the CaliforniaNevada boundary monument (Von Schmidt Survey), on Nevada territory. The project was to start the tunnel grade at a plane 20 feet below the lake's surface as found at that time, which was nearly the lowest water ever known. A fall of 4 feet was allowed for in the full length of the proposed work. The open cutting, 4,200 feet long, was projected to a depth of 57 feet at its heading, before the tunnel was to be entered. Taking the surface of the lake at 6,225 feet elevation, the summit of the range to be cut under was found to be 7,698 feet above sea level. The tunnel grade would be 1,275 feet below this ridge line. The open-cut work, it was anticipated, would be chiefly in soil, the tunnel work altogether in rock, for the most part probably granite. As projected, this work would debouch into Haines Canyon at a point about 3 miles from and about 1,500 feet above its opening into Carson Valley.

Tahoe outlet regulation dam.—As the survey first mentioned was made for the purpose of studying a scheme for drawing the water of Lake Tahoe to a lower level than the present, through a tunnel into Carson Valley, so the Tahoe outlet regulation dam survey was made to acquire data on which to estimate the cost of holding the water to a higher level than the normal, with the view of drawing down the surplus thus

impounded, through the natural outlet, for irrigation of the valleys along the Truckee River.

The intake of Truckee River from Lake Tahoe is about a quarter of a mile from Tahoe City. There already exists a framed timber dam in this channel at a point about 500 feet back from the lake shore line, which is owned by a company claiming the right to use waters of the lake for flushing logs down Truckee River and for other purposes. This dam has three open ways, closable by gates and flash boards, with a floor nearly on a level with the channel grade, and with 11, 12, and 10 feet clear width, respectively. It has a waste way with a crest 75 feet in clear length and 6 feet above the floor grade of the open ways.

The survey was made July 19, 1889. As subsequently found, the waters of the lake afterward fell during that summer about 1-2 feet, to an extreme low water in that autumn. At the time of survey the waste-way crest of the existing dam was 5:05 feet above the water surface of the lake. The survey section was made across the river channel, a few feet above the existing dam. The average height of the banks of the lake and river adjoining this section was found to be 8.5 feet above the lake's surface at the time of the survey, and the general elevation of the channel bed was 2.8 feet below the same water plane. To close the outlet to an elevation equal to that of the banks would require, it was found, a dam about 400 feet long.

As afterward ascertained by Mr. Hall, the lowest known water plane of Tahoe was in October, 1889, when, as above mentioned, the surface was about 12 feet lower than at the time of the survey in July of that year. The highest elevation of the lake's waters, as observed at Tahoe City, occurred in the spring of 1886, and was 53 to 5:5 feet above the extreme low water of 1889. The high water of 1888 was observed on September 8 at 1-85 feet, and that of 1889 was observed in the early spring of that year at 1:55 feet above the same datum. The high water of the spring of 1890 has been very nearly up to that of 1886, notwithstanding the fact that the outlet gates of the dam remained open during the rising period. These data are grouped here to afford some idea of the problem in

part examined by this survey. No survey was attempted of the Truckee River bed as the outlet channel of the lake with a view of commanding the lake's waters to a lower depth than the natural low-water plane.

Truckee reservoir site. The water-storage scheme, known as the Truckee reservoir project, contemplated a dam across the Truckee River at a point less than a mile above the town of Truckee, and about a quarter of a mile below the outlet of Donner Lake and Cold Creek into the river.

The survey consisted of meandering a level contour around the proposed reservoir space in the Truckee River canyon, and making a cross-section of the canyon at the proposed dam site. The contour was at a level 46 feet below the high-water plane of Donner Lake, as established by the reservoir survey next described. The dam section extended up to the plane of the contour only.

As surveyed, the dam for this reservoir to the height of the contour would be 1,131 feet in length and 70 feet in height above the bed of the Truckee River where crossed. The surveyed contour line was 30,290 feet in length. As demonstrated by this survey, water would be backed by this dam up Truckee Canyon about 23 miles to a maximum width of 1,500 feet, and would cover 206 acres in area. The chief waters which it would impound would be those discharged by the main Truckee River. Its utility is a little doubtful, as the work performed by it may be done by the utilization of Lake Tahoe as a storage basin. The Truckee reservoir site, however, has a great advantage over Lake Tahoe, in that it exposes to evaporation an infinitely smaller surface, and if it is shown by further investigation to be necessary to conserve the waters of the main Truckee, this will probably prove the most economical reservoir site for that purpose.

Truckee canal line.-Commencing at the dam site for the proposed Truckee reservoir as last above described, the Truckee canal line survey was carried out on the south side of the river to command the lands of Martis Valley, situated there, and commencing immediately below the town of Truckee. This canal line commenced at an elevation 20 feet below the top of