The Bull Pen is an old name for a small local valley encircled by 12 foot chain link & barb wire. Most of the fence has now been removed for garden fencing and chicken coops, but at one point it was used to house the ranch bulls. Out the back of it is a draw that leads up to a dead-end (unless you're a deer or willing to risk your neck) with a few unusual geological formations and a small cave. I've posted about hiking there before here
http://lapidaryforum.net/group/index.php?topic=1508.0 Didn't go all the way to the cave because I'm not quite as suicidal as my coworkers think I am and didn't want to navigate the scree slope below it when out alone, but it's a two-entry 'tunnel' in the base of a tuff monolith and while interesting also provides no usable shelter and not much else besides novelty.
The draw is close, too near the village for hunting, easily accessible and it's got some really cool material. Hiked all the way to the base of the rocks today just to see what's up there but the best material is about half-way up the slopes, in big chunks of float and a few exposed veins.
(The far hill is affectionately referred to as 'the boob' by my coworkers.)
Geology looks like basalt at the bottom, then purple welded tuff, then mudslide/lahar-like, then more pink welded tuff. Very fractured, big boulders have come down in a few places. Honestly there wasn't any material up along the rocks to make it worth the risk of going that high, but the iron staining on the rock was interesting. I think these are called 'liesegang rings'
https://en.wikipedia.org/wiki/Liesegang_rings_(geology) 
There's at least two broad bands of a milky purple material on the slope, but I wanted to find more of an agate that sometimes shows up in the float.
And if anybody ever says that a jasper chip with a three-cornered ridge down the middle must be man-made, they're lying. Natural fracture patterns will make chips that look very similar to tools and are just as sharp. There was anthropogenic activity in the area (a few bent rusty nails were found in the cave and a very old domestic sheep skull in the creek bottom) but no evidence that the jasper and agate here were previously mined.
This one is too big for my saw but looks promising so I carted it back anyway. I don't know what I'm going to do with it.
This one is bigger than it looked and is still up there somewhere because "I'll pick it up when I come back down."
A chunk of the a very nice vein, decidedly too big to be carted anywhere.
Slabs from one piece
Rough and slabs from another piece
And then it started to rain, so the saw went back inside!
