STRUCTURAL GEOLOGY OF EAGLE MOUNTAIN, AMARGOSA VALLEY, CA

Eagle Mountain is an isolated fault-block that consists of Cambrian carbonate rocks unconformably overlain by 13.4 Ma Eagle Mountain Formation (Niemi; 2001 GSA Bulletin). The mountain presently defines an open, steeply plunging fold (55,119) with a north limb that strikes N10W and a south limb that strikes N40E. Five sequential events can be determined through cross cutting relationships, fault orientations, and the angular unconformity. These events consist of 1) 10-15 degrees of eastward tilting, 2) open folding about a gently plunging axis, 3) deposition of sediments that form the Eagle Mountain Formation, 4) left-lateral, oblique normal faulting on west and northwest-dipping faults, and 5) further tilting of bedding to present day orientations. Early tilting is suggested by the angular relationship of the Cambrian rocks and the Eagle Mountain Formation. Folding likely pre-dated faulting because orientations of faults on each limb of the fold are indistinguishable. Rotation of Eagle Mountain to horizontal shows that the fold originated at a plunge and trend of 11°, 115. This rotation also suggests that many of the normal faults formed with original dips of about 70 degrees north-northwest. The cause of folding can only be speculated, but due to Eagle Mountain’s close proximity to the termination of the Furnace Creek fault zone, deformation may be attributed to movement of this fault.