A URI FERGUS GRA VELS— INDEPENDENCE HILL FLORA 897 



ing much of the Chico this Eocene erosion did not cut deeply 

 into the underlying older series of crystalline rocks. Certain of 

 the lower auriferous gravels underlying the lone formation near 

 the valley border may be Eocene or early Miocene, and the 

 same age may be assigned to the deep gravels of the upper 

 stream courses. 



Tlie early Miocene period. — About the time of the upper 

 Eocene or the lower Miocene, then, the shore line had retreated 

 far westward ; this is directly indicated by the occurrence of heavy 

 stream gravels brought up by volcanic agencies in the Marysville 

 Buttes along with estuarine Miocene beds, correlated with the 

 lone formation. These gravels carry comparatively coarse gold. 

 The slope of the Sierra had assumed the topographic character 

 which the Miocene and Pliocene deposits have preserved for our 

 inspection. The foothill topography of this old eroded surface 

 consisted of comparatively rough ridges, the level tops of which 

 indicated the old Cretaceous peneplain. The middle slopes con- 

 sisted of broad, partly longitudinal valleys and comparatively 

 gentle slopes in which the old peneplain is noticeable only in 

 places, such as Banner Hill, Oregon Hill, Osborne Hill, and the 

 tops of the hills of the upper Georgetown divide. The upper 

 slope reaching up the divide, situated very nearly where it is 

 today, on the west side of Lake Tahoe, consisted of rougher 

 and deeper valleys, divided by more or less level ridges, indica- 

 ting the old Cretaceous peneplain. English Mountain, the Black 

 mountains. Snow Mountain, Duncan Peak, Granite Chief, indicate 

 this Cretaceous peneplain in Nevada and Placer counties ; Mt, 

 Tallac, the Pyramid Peak range, Robb's Mountain and many 

 others indicate the same in El Dorado county. The relation of 

 the two eroded surfaces, the Cretaceous and the Miocene, is 

 clearly discernible from any point in the lower foothills looking 

 up toward the summit of the range. Above the deep canyons 

 of the modern gorges extend the broad, flat lava plateaux 

 capping the separating ridges and looking very much like an old 

 base level. These lava flows cover the comparatively gentle 

 topography of the Miocene valleys. Above them rise the peaks 



