Danville in Contra Costa County, California — The American West (Pacific Coastal)
Indian Grinding Holes
A Gathering Place for Food Preparation
Photographed by Joseph Alvarado, June 5, 2022
1. Indian Grinding Holes Marker
A short walk from here you will find sandstone outcroppings on which the Bay Miwok people who settled in this area many centuries ago ground acorns and other seeds into meal, slowly forming cup shaped depressions used as mortar holes.
Oak tree acorns have been a major food source for many California Indian groups. In autumn, baskets were filled with acorns then dried, cracked and shelled. Using bedrock mortars and rock pestles acorn was pounded into meal then leached of its bitter tannic acid. This fine grained meal was mixed in water, and cooked into soup or mush by placing heated rocks into baskets.
When you visit the grinding holes help protect these irreplaceable reminders of California's heritage by not walking on top of the rocks.
Erected by California Department of Parks & Recreation.
Topics. This historical marker is listed in these topic lists: Anthropology & Archaeology • Indigenous Peoples and Communities.
Location. 37° 51.034′ N, 121° 56.003′ W. Marker is in Danville, California, in Contra Costa County. It can be reached from Grotto Road north of Upper Rock City Road, on the right when traveling north. The marker is mounted to a metal stand in the upper parking
this page online
Regionally, this marker is in California’s San Francisco Bay Area and on the Coast Ranges. It is also on the American Pacific Coast. Globally, it is in North America, on the Ring of Fire, in the Pacific Rim, in the Western Hemisphere, in the Western World, and in the Anglosphere. Historically, it finds itself in what was once New Spain and also Mexicos Alta California.
Other nearby markers. At least 8 other markers are within 3 miles of this marker, measured as the crow flies: Blackhawk Ranch Quarry (about 500 feet away, measured in a direct line); Sentinel Rock Overlook (about 600 feet away); Turritella Snail Bed (about 700 feet away); Mount Diablo State Park (approx. 2.3 miles away); What Are Those Towers For? (approx. 2.3 miles away); Mt Diablo State Park (approx. 2.4 miles away); Whitegate Farm (approx. 2.4 miles away); Mount Diablo (approx. 2.4 miles away). Touch for a list and map of all markers in Danville.
More about this marker. In recognition of the mountains importance to our natural landscape, a state park was established in 1931. It was designated a National Natural Landmark by the National Park Service in 1982
This marker is part of the Trail Through Time series.
Also see . . .
1. Mount Diablo State Park. California Department of Parks and Recreation website entry:
"Mount Diablo is a dominant topographic feature in northern California. It was established in 1851 as the initial point of the Mount Diablo Base Line and Meridian for land surveys spanning two-thirds of California and all of Nevada. The mountains(Submitted on June 6, 2022, by Joseph Alvarado of Livermore, California.)summit boasts spectacular panoramic views."Photographed by Joseph Alvarado, June 5, 20222. Grinding holes low in the background
2. Trail Through Time. Mount Diablo Interpretive Association website entry:
"With 20 trailside interpretive panels, the complete Trail is 6.25 miles in length with a vertical elevation gain of 2,940 feet."(Submitted on June 9, 2022, by Joseph Alvarado of Livermore, California.)
Photographed by Joseph Alvarado, June 5, 2022
3. Grinding Holes
Photographed by Joseph Alvarado, June 5, 2022
4. Nearby natural history marker
Photographed by Joseph Alvarado, June 5, 2022
5. Sandstone Caves
Credits. This page was last revised on August 2, 2025. It was originally submitted on June 6, 2022, by Joseph Alvarado of Livermore, California. This page has been viewed 2,120 times since then and 151 times this year. Photos: 1, 2, 3, 4, 5. submitted on June 8, 2022, by Joseph Alvarado of Livermore, California. • Syd Whittle was the editor who published this page.
