I'm not really sure I have a favorite place to dive at Folsom. I once had a phenomenal dive at the dam overlook point. We had 20' visibility, which I haven't experienced since then. Unfortunately due to heightened security (read: they didn't want to spend the money to strengthen the dam for the 20,000+ cars per day, and used terrorism to skirt the issue), you can't get there without a boat (i.e. the thing terrorists would use to blow up the dam).
There are basically 4 locations at the lake that we dive.
1. Hobie Cat Boat Ramp at Brown's Ravine
2. To the right of the small boat ramp at Granite Bay
3. Out past the swimming beach at Granite Bay
4. Rattlesnake Bar
Hobie Cat Boat Ramp is a nice place to dive when the water is a bit higher. We've had the people at Brown's ravine kick some of our divers out of the area because they said we weren't suppose to use the boat ramp as an entrance point. Visibility is in the 2' to 10' range.
The nice thing about Hobie Cat Boat Ramp is that you're basically diving over concrete and asphalt when the water level rises, so there isn't as much of a silt out as other locations.
The two locations at Granite Bay are nice, but you get a lot of boaters that you need to look out for. Visibility is between 2' to 15' at times, but don't count on the 15' vis that often. Alhough a dive flag isn't required by California law, I strongly recommend you use one. The boaters won't have a clue as to what the dive flag is, but at least they'll be going slow when they try to steal it. (this happens more often than I'd like to admit)
Rattlesnake Bar is probably the place we dive most frequently. The visibility is in the 2' to 10' range, but often it's between 2' to 4'. Lights come in handy when trying to locate your dive buddies.
We like Rattlesnake Bar because you're able to dive in coves that are 30 ffw to 50 ffw, and since the coves are narrow, the boaters and jet skis are suppose to keep there speed at 5 mph within 200' (?) of the land. That doesn't mean they do this of course, but so far they seem to keep their distance. We dive this location usually once a week for practice and fun.
Overall Folsom is a mediocre dive site. I know of a few spots on the lake that might be cool to check out with a boat, but I probably won't boat dive at Folsom any time soon.
I can't emphasize watching for boats and other water craft enough. We really focus on surfacing at the dive float, and on the off chance we can't find it, we shoot a surface marker buoy/bag. I'm not saying that this will insure your safety, but it's worked well for us so far.
I know of a few people that dive Beales Point (sp?), but since I haven't dove that location, I'll let them tell you about their experience.
I have a few photos in the Trip Report section of our site that you might find interesting.
www.sauedir.com
Hope the above helps. We're heading up to Stumpy Meadows tomorrow morning (6/20/04) at 6:30 am for a couple of quick dives.
~ Jason