The 4,000 was a type but the 400' is actually that deep from the top of the water to the bottom of the lake. An no Joe, that isn't the elevation as it is higher than that. That is one reason they don't worry much about divers going down to that old town and taking artifacts and when the lake is low and the town is above water they have guards around it to stop anyone from doing anything but taking pictures. Only 3 times since I have been here the lake has been low enough for it to be above water but the last time when the lake reached its all time low a lot of the old towns and railroad places and Indian Cemeteries were above the water. The sheriff's department boating division kept a constant patrol to keep people out and then closed the canyons as the water was to low for boats.
EDIT: I hope I can get this in. Joe the Dam is 602 feet high and when it is full and the Drum Gates closed that means the water has to be at least 600 feet deep at the face of the dam. Some of the other areas in the canyons may be less or more depending on which canyon branch you look at.
Ron