Lilly Lake (a.k.a. Glen Alpine Lake), is in the wilderness area above Fallen Leaf Lake, which is above Lake Tahoe.
This is the headwater to Glen Alpine Falls.

This was taken around 11:30 AM on May 4th, 2011, after a record winter snowfall. When there isn't snow you can drive up here, but there was still over 3 feet of snow on the ground. This made for a long uphill trek, sometimes in snow over knee deep.