GEOLOGIC HISTORY. 
71 
accomplished intermittently, to the deposition of the Chemehuevis 
gravel and the following minor epochs represented along lower Colo- 
rado River. Whether so close a parallelism of events is warrantable 
or not, it is evident that the general sequence of events as recorded 
in the Bonneville basin is similar to that of the Colorado Valley. 
Comparison with southern California. — Hershey a has arrived at a 
conclusion regarding the length of Quaternary time and the com- 
plexity of its history which is similar in a general way to that shown 
by the epochs of the Bonneville basin and of western Arizona. Prob- 
ably the most significant feature of his subdivisions in relation to the 
phenomena of western Arizona is a long epoch of erosion at the begin- 
ning of the Quaternary, which in his opinion is much longer than all 
the subsequent epochs combined. This epoch may, on further 
study, prove to be equivalent in point of time to the erosion of Grand 
Canyon. 
Comparison with the Pacific coast. — In studies of the marine beds 
of the Pacific coast, Arnold b shows that, while the epochs of the Ter- 
tiary and Quaternary are very fully represented, the subdivisions do 
not conform in all cases to those of the standard time scale. The 
division of Tertiary time as given in his publications, which in per- 
sonal interviews he asserts will hold good for the Pacific coast gener- 
ally, is shown in the following table: 
Correlation table oj 
the marine Tertiary 
and Pleistocene formations of the Pacific coast. 
Period. 
Epoch. 
Formation. c 
Quaternary 
Pleistocene \ 
San Pedro, 1,000 ± feet. 
/Pliocene J 
Merced, 5,000 ± feet. 
Transitional.. 
Purisima, 800 ± feet. 
Miocene 
San Pablo, 1,500 to 2,000 feet. 
Monterey, 2,500 ± feet. 
Tertiary 
Oligocene 
Vaqueros, 3,000 ± feet. 
San Lorenzo, 2,300 ± feet. 
Tejon, 4,000 ± feet. 
Martinez, 1,000 to 2,000 feet. 
oHershey, O. II., The Quaternary of southern California: Bull. Univ. California Dept. Geol., vol. 3, 
1902, pp. 1-30. 
b Arnold, Ralph, The Tertiary and Quaternary pectens of California: Prof. Paper I '. 8. Geol. survey 
No. 47, 1900, p. 9. 
cln this column full lines represent unconformity; broken lines, conformity. 
