Upper Jackass Lake hosts unbelievably gorgeous alpine granite. The hike in isn't trivial, but once you're there, you'll never want to leave. What's more, there's tons of great swimming and cliff-jumping.
From Bass Lake, head up Beasore Road for about 1 hour, then park at Jackass Trailhead. Follow a very steep trail for about 2 miles till you arrive at Lower Jackass Lake (note: there's an incredible jump-rock here over the lake), then follow the sign and cairns to upper Jackass Lake. You may lose the trail from time to time, but all you have to do is trend uphill and you'll eventually get there after passing Middle Jackass lake. Total hiking distance from is about 4 to 5 miles.
Once you get to the lake, walk to the Northeast end of the lake and find a campsite with a large, very obvious flat rock locally known as "table rock." With your back to the lake, walk straight back into the woods till you find "The Prowt," the first of the Upper Jackass problems. The rest of the problems are another 100 meters further.