There are two topo maps available but cover a limited area of the lake. One is for Humboldt Bay and the other is the area around Treasure Island I think.
The chips are very generic and show no top lines or depths that I have seen. The maps that cover the entire lake show mark areas where you could strike a rock but are some what vague. Keep in mind thelake elevation changes depending on diversions to the Jackfish river and time of year.
Thanx