AURIFEROUS DEPOSITS—PLAIN-GRANITE—CLAY SLATE. 
261 
is not clearly marked by lines of deposition or stratification, but appears to be regularly stratified. 
Some of tbe layers are nearly white or gray. 
Many shafts have been sunk into these rocks in search of the “lead” or “pay-dirt,” but without 
any success. The layer of auriferous drift, however, appears to underlie these strata, for tunnels 
are excavated at the base of the hill and extend under it. Whether the drift was washed under 
the edges of these strata, or does in reality underlie them, being older, I could not determine in 
the short time devoted to the examination. The strata appear like the Tertiary of Ocoya 
Creek. 
August 10.— Mokelumne Hill to Sacramento. —Left Mokelumne Hill at four in the morning, 
and descended a long hill to the level of the Mokelumne river, which is spanned by a neat and 
well-constructed bridge. The surface of the country in the vicinity of lone Valley is rounded 
and undulating, and is covered by oak openings. The soil is good. The bottom-land of the 
Cosumnes River is very broad, and well wooded with groves of oak. There is a wide area of 
excellent agricultural land at this place, and many fields are enclosed with board fences. The 
river is a stream of considerable magnitude and flows slowly. It is crossed by a suspension 
bridge in one span. 
After crossing the alluvial plain bordering the stream, we rise up to the level of the wide and 
regular slope, which is without trees, and, at this season, appears perfectly barren and desert¬ 
like. It is in all respects like the same slope further south along the San Joaquin. Distant 
rivers are indicated by long lines of trees, that sometimes loom up by mirage and appear to be 
suspended above the verge of the horizon. We traversed this broad plain towards Sacramento, 
stopping at three stations, where water is obtained for the horses from wells. 
Sacramento is located upon the alluvial deposits of the river, and is surrounded by a levee to 
prevent inundations. Oaks and cotton-wood are the prevailing trees. 
SACRAMENTO TO YANKEE JIM’S. 
August 12. —Sacramento to Auburn, 40 miles. —We traversed the long and gently ascending 
slope towards the mountains. At Oak G-rove, about ten miles from Sacramento, the surface is 
undulating and is covered with groves of oak of two species : ( Quercus macradenia , Torrey, 
probably Q. Hindsii, Benth.,) and Q. agrifolia. 
Granite crops out along the road about twenty-five miles from Sacramento. It corresponds 
very nearly with that obtained from the banks of the American River at Mormon Island. It is 
traversed by feldspathic, or coarse granitic veins like those at Monterey, and weathers into 
large, rounded blocks, which rest like great boulders on the surface. These are very abundant 
in some places, but are the result of slow decomposition alone ; they are not transported masses. 
There appears to be a very thin layer of drift or auriferous earth in this vicinity, and mining 
operations are in progress on some of the flats. 
About four miles from Auburn outcrops of clay slate were passed, and one of the ridges is 
covered with loose, boulder-like blocks of basaltic rock, probably derived from a layer in place. 
Auburn to Yankee Jim's, 22^ miles.—On leaving Auburn the road immediately ascends a 
ridge formed of the vertical layers of clay slate. This formation continues to the American 
River, which has cut its deep channel or canon in it. The sides of the canon are abrupt and 
precipitous, and probably are not less than 35° in inclination at any point in the vicinity. 
The road is constructed from the summit of the divide (or plateau between the streams) down 
