•448 University of California Publications in Geology [Vol. 7 



section, as are also fine materials similar to playa lake deposits. 

 The very coarse fanglomerates lack matrix and are but little 

 cemented. The more finely textured upper members are com- 

 monly sufficiently indurated to permit erosion into a gullied 

 topography with steep fluted walls. 



Where the fanglomerates can be observed lying on the older 

 rocks — plutonics and pyroclastics — as east of Afton, the surface 

 upon which they rest is one of erosion and often has considerable 

 relief. It is not known what relation in time this erosion interval 

 has to the development of the Ricardo erosion surface, which 

 truncates the folded late Miocene strata of the Mohave Desert 

 fifty to one hundred miles to the west, as described by Baker. 9 



Pleistocene Lacustral Beds 



Areal Extent. — The Manix Beds cover an area of irregular 

 outline, measuring twenty to twenty-five miles in length, and of 

 not less than two hundred, perhaps more than three hundred, 

 square miles extent. (See pi. 22.) 



The southeastern limits of the lake-beds are not definitely 

 known. To the south they extend nearly to the flanks of the 

 Kane Mountains. To the west the deposits reach almost to Kouns. 

 To the northwest their limits are not certainly determinable, but 

 beds of similar aspect and containing similar molluscan shells are 

 reported by Mr. S. H. Gester to occur along the west flanks of 

 the Alvord Mountains. To the north the Manix Beds are known 

 to extend to the foot of the waste slopes stretching southward 

 from the base of the Alvord Mountains ; farther east the northern 

 border of the beds bends around the south end of the ridge on 

 which Field is located, and passes along the south front of Dunn 

 Mountain and the west face of Cave Mountain. 



The limits of the beds to the northeast are significant. The 

 underlying fanglomerates, because of deformation, arch over the 

 older rocks just east of Afton, but the lacustral beds are limited 

 to the west side of the arch. The eastern edge of the deposits 



9 Baker, C. L., Physiography and Structure of the Western El Paso 

 Range and the Southern Sierra Nevada, Univ. Calif. Publ. Bull. Dept. 

 Geol., vol. 7, no. 6, pp. 137-139, 1910. 



