This morning I rode from Encanto Park to Crystal Lake. This was my 2nd time. I got a pretty early start (on the road at 7AM). I was the only one out on the climb. On my descent I saw only 2 cyclists past the gate. On the lower slopes (near East Fork) I saw a few riders heading up.
Personally I think the Crystal Lake climb is more challenging than GMR. The descent (especially on the closed section) is very fast and you can use the whole road to pick the best line when cornering.
My impression is that GMR is more popular than CA39, why is that?