I have been unimpressed with Victorville bike shops so far. But most bike shops leave me cold.
I walked into an Orange County shop once, I believe it was Switchback Cyclery. They seemed to be friendly, and knowledgeable. But the general problem is that every kind of yahoo may be working at a bike shop, and often gives you inappropriate advice, tries to sell you on the newest, baddest gear, and is interested only a teeny bit in hearing what you will be doing with the bike. Brian, if I'm being too harsh, go ahead and say so, but I wouldn't be surprised if you agree.
If I was going to look for the Standard TM aluminum hardtail with Deore or LX parts, then most places have this. REI is not a bad place to go to, but if you want to patronize a small shop I hear the Path and Switchback in OC are good shops. You can check out reviews and directions to shops on mybikesite.com in the So Cal section. There is one shop in Pasadena I want to visit some time, because the guy appeared to have some very good New Old Stock frames that he could build up for a decent price.
There are a few things I'd look for. A bike, especially a mtn bike, needs to be comfortable, but many shop guys will try to put you on a bike too small for you. I remember I bought my first bike from Sport Chalet (they still source Marin bikes, which are good bikes, but I would never buy from them now) and the employee tried to put me on a 19" frame, and my friend with me thought I should get it. But I tried the 21" (which had plenty of standover clearance) and it felt better, much better. The employee, who later became a roommate, oddly enough, couldn't imagine anyone but a giant riding it. I now know that he was operating on received opinions, mostly from people who race full-time, and hadn't been properly trained. Well, I bought the 21" bike and rode the hell out of it in Wrightwood, everyday, for a whole summer on any trail I could find, including the ski slopes. I used it for years at a campus bike, and now my brother rides it everyday everywhere. I know many people who buy a mtn bike a size too small, and ride it for a while and that's it. They feel squeezed, and uncomfortable, but they don't know why. So it gets abandoned, sold, and handed down to someone else.
The second thing that matters to me is the parts and how to maintain them. I've had every kind of brake out there, and despite some great rides with disc brakes (in Moab, among others) I think they're a pain to adjust and unnecessary. I prefer brakes that are easy to set up and inexpensive to maintain, like cantilevers and v-brakes. I prefer a 8 speed cassette because of the thicker chain and better shifting IMO (although 9 can be set up very well, I know). The handlebar is overlooked by most customers, but different handlebars make such a huge difference. Most mtn bikes sold today have suspension forks, and I'd prefer a heavier, maintenance-free fork versus some light wunderkind that has a zillion parts to maintain.
There's a ton of other long-term considerations, but the standard, aluminum hardtail is pretty much built in the same factory in Taiwan, sometimes with minor differences, and sold with different brand names in almost every shop with mtn bikes.
BTW: My wife has a Jamis Exile, normally $900 but Performance regularly discounts it to $500 around now, and it is a screaming good deal. It is well thought out.
IF you're doing your research, Dirtragmag.com has the best reviews of bikes for a magazine, and I like the user reviews on mtbr.com