This report is one of the most valuable produced by the survey. During the year the great area in California which lies below the level of the sea was examined to ascertain whether it could be filled and maintained as a lake by a canal from the Colorado river, and the decision is in the negative. The depressed area covers about 1,600 square miles in California, and the difference between the rainfall and the evaporation is so small that if the whole Colorado river were poured into the basin, it would cover only 556 square miles of surface, or little more than one-third the basin. Filling would cease at that level for the reason that the whole supply of the river would disappear in vapor. The slope of the Colorado river is extraordinary, 2.13 feet per mile at Stone's Ferry, and 1.21 feet at Camp Mohave, which may be compared with eight inches, the average fall of the Mississippi per mile. At Stone's Ferry the velocity is 3.217 feet per second and the discharge 18,410 cubic feet. Great difficulties stand in the way of the proposed canal, and the engineers do not think the lake, if it could be formed, would have an appreciable effect upon the climate of the surrounding region. The primary object of this survey is to carry the grand triangulation of the continent across the country under its jurisdiction, and to map the surface so as to enable the Government to put the ground properly in market. In addition to these objects a great amount of valuable work is done in geology and natural history. Prof. Jules Marcou, geologist attached to the survey, points out that the valleys of Santa Clara and Santa Barbara in California may become the site of _true_ artesian oil wells. The ordinary flowing oil well is supposed to obtain the force which lifts its oil above the surface level from confined gases in the earth, but in California the lift will be obtained in precisely the same manner as in the case of artesian wells for water. There are strata of sandstone impregnated with the petroleum, and these strata are lifted up on the mountain sides, so that a well bored at a low point in the valley would be supplied from a reservoir some thousands of feet high. The wells will have to be about three thousand feet deep.