I had a great time hiking in this park, especially with the nice winter weather! I hiked up the Mormon Trail and walked around to Hidden Valley Fat Man's Pass that actually loops around the Hidden Valley Tunnel, taking you back to the top of the Mormon Trail!
Had a great time clambering up the rocks and exploring and taking picture. Beware though, I could see a lot of places on the trail getting pretty slippery when it rains and actually getting dangerous. Especially when some parts of the trail seem to merge with a wash.
Saw a ton of families with grade school age kids on the Mormon Trail, more experience hikers on the Hidden Valley loop. Lots of fun picture opportunities and the hike is not bad for new hikers. Watch out coming down the Mormon Trail though, it's steep and rocky, and my friend tripped over on and had a close call with her ankle on the way down.
It's free to do, but the parking lot on a Saturday mid morning at the Baseline/24th trailhead was crazy, we had to park down the street. Also, the park is free! Have fun!