Obsidian question

[aa battery]

I live in the central valley in California and i found so much obsidian its crazy in my back yard. I have many small pieces but 3 of them are over 10 lbs . Behind my home is a very old creek now used for irrigation . The sand here is about 20 feet deep and large rocks were found at 6 feet. I met an old guy that helped build Fresno State University and he found a ton of obsidian on site. There must of been a volcano in the Sierra mountains but where ?

 

[rodoconnor]

All over, but strangely enough the town of Volcano is not one. It's limestone that has decomposed.

 

[DDancer]

Try checking out the various geological society sites and ones dealing with volcanism. You might find what your after however you could very well have a placer type deposit of the obsidian on your property as well. Some pictures would be interesting.

 

[aa battery]

thanks

 

[Moesia]

Depends where you live you cited an enormous area , here is the base geologic map.

https://ngmdb.usgs.gov/ngm-bin/pdp/zui_pdpViewer.pl?id=7654

Look where you live and compare.