. Bulletins of American paleontology. Baja California SrRAriGRAPH\: Carreno and Smith 65. Text-figure 40.—Split Mountain Gortie. Miocene reddish-brown alluvial tan deposits exposed in Fish Creek Wash. View west at rocks that Woodward ( 1974) referred to the Anza Formation (Bor- rego Mountain SE 7';-miniitc quadrangle SE '4, NW '4 Sec. 2.*^. T S. R S E). The alUiNial sediments underlie the "lower houlder ; which are now regarded as a stur/strom in the Split Mountain Formation (D. R. Kerr, written communication, 2004). Photo, J. C. hmle. Jr. Gypsum, as seen on the geolo
. Bulletins of American paleontology. Baja California SrRAriGRAPH\: Carreno and Smith 65. Text-figure 40.—Split Mountain Gortie. Miocene reddish-brown alluvial tan deposits exposed in Fish Creek Wash. View west at rocks that Woodward ( 1974) referred to the Anza Formation (Bor- rego Mountain SE 7';-miniitc quadrangle SE '4, NW '4 Sec. 2.*^. T S. R S E). The alUiNial sediments underlie the "lower houlder ; which are now regarded as a stur/strom in the Split Mountain Formation (D. R. Kerr, written communication, 2004). Photo, J. C. hmle. Jr. Gypsum, as seen on the geologic map hy Kerr and Abbott ( 1^96). Rapid movement of such massive deposits (hun- dieds of miilons of cubic meters) from adjacent moun- tains to emplacement would have taken minutes, hut the time-frame for this catastrophic event can be esti- mated from adjacent units. Kerr and Abbott (1996) reviewed microfossil data from overlying marine sed- iments and estimated that the rock fall and rapid How occurred at ± Ma. Fish Creek Gypsum. Late Miocene.—The Fish Creek Gypsum, long regarded as a nonmarine evapo- rite, has claystone intercalations that contain Late Mio- cene. Ma microfossils typical of a normal sa- linity environment (Dean, 1996; McDougall. oral com- nuinicalion. 1998). Peterson and Jefferson ( 1997) suu- gested the gypsum could have been deposited near a high-temperature hydrothermal vent. The deposits rep- resent the second of three seawater incursiiMis in the northern ancient gulf, and the earliest seawater in the Fish Creek Mountains area; they coiielale with the lower Imperial Formation section east of the White- water River. Dean (1996) regarded the Fish Creek Gypsum as a facies of the Imperial Formation because both units are marine and have similar fossil assem- blages. A rock slide megabreccia of basement rock above the Fish Creek Gypsum was called the upper fanglom- erate by Woodward (1974). upper boulder bed by Winker (1987). and upper br
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