356 



University of California Publications. 



[Geology 



them to the Eocene period. Although the Black Mountain local- 

 ity where Fairbanks collected leaves which were determined to 

 be of Eocene age by Knowlton was not visited in the present 

 reconnaissance, mammalian fossils of upper Miocene age, as 

 determined by Merriam, were collected in the bluffs just west of 

 Ricardo postoffice. 



At the mouth of the canon very light brown, rather fine 

 breccia beds, showing imperfect bedding and cross-bedding, dip 

 in a northerly direction. They are overlain by a thin bed of 

 massive purple breccia which seems to be faulted against a lava 

 by a strike-fault. The lava continues for about a mile up the 

 canon, which has cut a deep and narrow gorge through it, and 

 then gives way to sediments which overlie uneonformably the 

 lava. Two miles to the east the basal beds of the sediments rest 

 on granite. The basal sediments are predominantly dark red 

 breccia, with thinner interstratified layers of light gray color, 

 the whole aggregating approximately 250 feet in thickness. Next 

 in the upward succession comes a light pink volcanic breccia 

 forming one massive bed 100 feet in thickness, and cut by two 

 strike-faults of fifteen and fifty feet displacement. This is suc- 

 ceeded by 150-250 feet of beds mainly gray in color, but with 

 thin interspersed layers of dark red. Then come 300 feet of 

 light gray, rather fine, poorly stratified breccias, capped by a 

 flow of vesicular basalt about fifty feet thick. The outcrop of 

 this flow is repeated by a normal strike-fault, and its upper 

 surface has been eroded, as is shown by its rough floor, its vari- 

 ations in thickness, and by particles of the basalt in the over- 

 lying beds. The beds just under the basalt have been baked to 

 a red color. The basalt forms a narrows in Red Rock Canon 

 just below the Ricardo postoffice. The beds below the basalt 

 weather into badland forms reminiscent of Gothic architecture, 

 examples of which are shown in plate -40b. 



Above the basalt the material is for a few feet fairly well 

 assorted and stratified and has probably been deposited by water. 

 This is succeeded by light bluish-gray tuff and breccia inter- 

 stratified with light yellowish-brown beds of the same composition 

 and texture, the whole containing much fine gravel, and having 

 an unknown thickness. The beds are more massive in character 



