Photographer: Bob Tregilus 
Summary Author: Bob Tregilus 

Indian Rock is a Miocene-Pliocene olivine basalt monolith on the north end of the Smoke Creek Desert, Nevada, just west of the town of Gerlach. The lava that formed the Modoc Plateau, surrounding the borders of what’s now California, Nevada, and Oregon, squeezed up through a small vent some 4 million years ago. Then, during the Pleistocene glaciation cycles, from 2.5 million to 12,000 years ago, this monolith was repeatedly submerged under prehistoric Lake Lahontan, as the ice sheets grew and melted. During this time, it was encrusted with tufa from bubbling mineral springs.

Since the last ice age, it’s been exposed to water, ice, and wind erosion, shedding its mantle of tufa in the piles seen around its base. So once again the basalt has been exposed. Note that the tufa is the light-colored rock and basalt is the red/black-colored rock. Sagebrush at bottom left can be used for scale purposes. Photo taken on March 12, 2018.

Photo Details: Camera: SONY ILCE-7RM3; Software: GIMP 2.10.12; Exposure Time: 0.0050s (1/200); Aperture: ƒ/13.0; ISO equivalent: 100; Focal Length (35mm): 24.

• Gerlach, Nevada Coordinates: 40.6516, -119.3568
• Related Links
  • Hvítserkur, an Iceland Sea Stack
• Student Links
  • Geologic Time
• Earth Observatory
  • Pyramid Lake, Nevada