(lb)
Looking at the two DUMBS maps I have, here is a better visual on possible tunnel routes. The red route would theoretically go from Edwards to Palmdale to Catalina. The yellow route would theoretically go from Edwards to Catalina directly. In my research, there is supposedly a DUMB at El Mirage, which is East of Edwards. So, where the actual route may go is open for debate. Maybe it goes more to the Seal beach area?
Looking at the underwater topo map, you can see the terrain a tunnel would have to cross. Near Seal Beach are a couple of interesting features underwater.