Hi Mike, The sandtraps are on the creeks running into the LA aquaduct. Los Angeles gets most of it's water from the Owens Valley in Eastern California. The LADWP dredge the creeks, making ponds with a small dam and gate to adjust the outflow. The sand and debris is trapped in the pond allowing "clean" water to drain into the aquaduct. Some of these traps are up to 200 to 400 feet long, 20 t0 40 feet wide and maybe 10 to 20 feet deep. The DFG usually stocks these ponds regularly during the open season. I like them if I have grandkids or newbies with me because they usually don't have much vegetation and are easy to fly fish for kids. They are also good tourist traps, keeping them off the creeks farther up where we like to go. Jim