Yup, that's Devil's Postpile. There are also some further north off HWY 108 that you can walk up to. I have some pictures I took of those somewhere.

There is also "Fossil Falls" right off 395 which is the area I was thinking of when I thought of basalt flows. The whole area has dramatic outcroppings. https://en.wikipedia.org/wiki/Fossil_Falls

I'm not a geologist, scientist or academic, I just appreciate geology and collect minerals. I need to write about some fantastic things in California that the majority of people don't know about. Thanks for the inspiration. Followed.