THE TOPOGRAPHY OF CALIFORNIA 573 
place the San Joaquin and Sacramento rivers, which are the 
principal streams of the valley, are confluent and flow westward 
through the straits of Carquinez, thence through San Francisco 
Bay into the ocean. Well borings at different places over the 
valley show the upper 1000 feet or more of the valley deposits 
to be fluviatile and subaérial,' for the strata consists of alternat- 
ing beds of sand, clay, and gravel, and in places contain loess- 
like? strata and organic remains} of land and fresh water animals. 
The origin and growth of the valley, as stated by F. L. Ran- 
some, is in brief as follows: 4 
With the post-Pliocene elevation of the crest of the Sierra and with the 
gradual upward diastrophic movement of the Coast Ranges during Pleistocene 
times . . . . the valley became closed in by mountains as we find it at the 
present day i... s 6 
All through Pleistocene and recent times, the streams flowing down from 
the Sierra, and from the eastern slope of the coast ranges have been pouring 
detritus into the deepening valley, depositing the coarser materials in broad 
alluvial fans and carrying the finer silt farther out to be spread over the plain 
in flood seasons. 
So it seems that this area has been largely built up at equal 
pace with its subsidence, usually existing as a low, marshy tract, 
retaining a large part of the detritus brought down from the 
Sierras and Coast Ranges. The southern end of the valley is a 
low, marshy area, with no well-defined outlet, and at the present 
time retains all the detritus and sediment brought there from the 
adjoining mountains. 
The Sterra Madre Mountains.—\t has been noted that west of 
the California Valley the axes of the coast ranges run nearly 
northwest and southeast, but the further continuation of the 
coast ranges to the southward is first marked by almost east and 
west axes, which are in turn followed by ranges running north- 
west and southeast. In each case the coast line turns and runs 
parallel with the axes of the mountains along the coast. The 
«Eighth Ann. Report Calif. State Mineralogist, 1888, pp. 558-560 ; Tenth Report, 
1890, pp. 548-564; Twelfth Report, 1893, pp. 350-351. 
? Bull. No. 3, Calif. State Mining Bureau, p. 16. 
3 Bull. No. 3, Calif. State Mining Bureau, pp. 20 and 68. 
4The Great Valley of Calif., Bull. Dept. Geol. Univ. Calif., Vol. I, p. 398. 
