You should have an Adventure Pass, especially if you plan to stop anywhere, even for a short time. The last few times I've been there the rangers do take that seriously.
By the way, if you have an annual National Parks pass you can use that, they're good for all Federal lands that have this sort of fee. There is a paper holder you can hang from your rearview mirror that holds the pass and displays the number. I don't recall the current rates, but a one-day Adventure Pass used to cost around $5, with the annual around $35, and the annual National Parks about $80 (unless you qualify for one of the discounted rate ones). If plan to hit a National Park or two in next 12 months and you plan to be in the various So Cal forests, the NP pass is not a bad way to go.
The view from the top of the Los Pinos fire lookout is nice, definitely worth the drive. Espinosa is a fun trail, but changes often. Do check with the rangers before heading down that way. Also, I'm guessing fire danger is pretty high right now.
Part way down Espinosa when the club went there in July 2006, the day before the start of the big fire that closed the area for a few years. More from that trip at this gallery:
http://frankbaiamonte.smugmug.com/So-Cal-Club-Xterra-SCCX/Corral-Canyon-Espinosa-Jul/
From the fire lookout tower, July 2010.
Have fun, and let everyone know how it goes.
