In March 2002, I went for a 2 hour trip into the Hell Hole cave located near the UC Santa Cruz campus. My good friend led the way. Here are some nice pictures.
 

Sitting in the woods near the cave
 

Sitting at the entrance, it's on the side of a steep hill. The entrance has a metal grate over it. You can't be too big if you want to get inside. 
 

Suited up with lights, pads, and old cloths, we're ready to go in.
 

Inside the cave it's really tight!
 


We saw a 5" giant pacific salamander too. (ok, just Geiss saw it.)
 

It wasn't all cramped in there, sometimes one of those little holes opens up into a big room!
 
We also saw quite a lot of quartz, one cavity of the cave was a large geode. There is quite a bit of human evidence, specifically clay sculptures.