Report 6712: Campers hear complex vocalization

June 1994, West bank Chopaka Lake, 2-3am.  I awoke to the most god-awful "animal" voice I've ever heard. My friends slept through it and teased me the next day when I described the sounds. However, they stayed the next night after I left and reported to me later that they were awakened as I had been and were quite frightened by the same sounds at around the same time. Just today I first heard of sightings by others at the lake in '96.  The sound I heard was very loud, echoing across the lake and the hill on the east shore.  It originated from the NW corner of the lake. The "call" was a good 10 secs long each time starting off with a very low register bellow like the bellow of a bull or elephant, then morphing into a cougar-like snarl and then finishing similar to an eagle screech, several octaves rise in a single voicing! There were a couple obnoxious bulls in the area in the daytime but their bellowing was normal and familiar.