THE MIOCENE PERIOD 811 



are found in some parts of the Coast Range 1 of California up to 

 elevations of 2,500 feet. 



Non-marine deposits. The sea seems not to have overspread 

 the northern part of the central valley of California when it did 

 the southern, and at the north there were deposits of estuarine, 

 lacustrine, and probably subaerial origin (lone formation) contem- 

 poraneous with the marine beds farther south. They consist of 

 the common sorts of clastic sediments, with some coal, iron, etc. 



Along the east side of the central valley of California, auriferous 

 gravels, 2 brought down by streams from the Sierras, were being 



Fig. 545. Section showing the structure and relations of the Miocene sys- 

 tem in the San Luis Obispo region of southern California. Jsl, San 

 Luis formation, Jurassic; Nm, Monterey shale, Miocene; Nrt, rhyolite 

 tuff; Np, Pismo formation, Miocene (?); Npr, Paso Robles formation, 

 Pliocene; Pal, recent alluvium, etc. 



deposited in the lower courses of the valleys during at least a part 

 of the period. These gravels seem to have been deposited on a 

 surface of slight relief, interpreted as a peneplain. 3 The tilting of 

 this plain toward the end of the Miocene seems to have quickened 

 the upper parts of the streams and caused them to deposit gravel 

 below. The Sierra Mountains are thought to have been at least 

 4,000 feet lower than now when these gravels were deposited. 

 From some of the gravels of California, thought to be of Miocene 

 age, human relics have been reported, 4 but there seems to be the 

 best of reason for doubting their authenticity. 



Non-marine Miocene beds are rather wide-spread in south- 



1 Lawson and Palache, Bull. Dept. Geol., Univ. of Cal., Vols. I and II; 

 Ashley, Jour. Geol., Vol. Ill, p. 434; and Fairbanks, Jour. Geol., Vol. VI, p. 

 561. 



2 Whitney, The Auriferous Gravels of the Sierra Nevada of Calif. ; Turner, 

 14th Ann. Kept., U. S. Geol. Surv., 1894; Lindgren, Jour. Geol., Vol. IV, 

 1896, pp. 881-906; Diller, Jour. Geol., Vol. II, pp. 32-54. See also folios 

 of the Gold Belt of Calif., U. S. Geol. Surv. 



3 Diller, Jour. Geol., Vol. II, pp. 33-54. 



4 Whitney, op. cit. 



