Look at the SEA sectional and follow V204 from OLM to YKM. As you are tooling along VFR with FF you will have a section of that route where radar services are terminated because you are shadowed from their radar by Mt. Rainier. You leave the transponder alone as you will emerge from the shadow on the other side and you still need the code. Unless the controller says "Squawk VFR", leave the code alone.
There are places in California where that happens if you are at the MEA, and some of them are not even behind tall mountains.