Tidbit
There are old gold and quartz mines nearby.
Location marked on this map
info:
https://mrdata.usgs.gov/mrds/show-mrds.php?dep_id=10109115
info about mine shafts, etc
I have seen similar rock all over gold country in both Kalifornia and Nevada. I always collect samples for testing for gold. It breaks easily with a hammer and I grind it in old kitchen blenders.