If it’s just GMR to the shack, the ride profile 5-7% grade straight to the top, 2500ft. Even for a beginner, it’s about 2 hours round trip.
I was just there last night. Couple safety warnings aside from the obvious:
1) on the descent, take your time and be conservative, especially if it’s your first time. A couple of the turns are negative decreasing radius turns. Meaning, they tighten the further into the turn you go.
2) Rock debris is always unpredictable. We live in SoCal which sits on tectonic plates. Even if the road is clean when you go up, that doesn’t mean the road will be clean when you go down, so watch for loose rocks, big and small. Even if the debris isn’t big enough to make you fall, they can still puncture and blow your tire, which WILL make you fall, asleep specially if you are leaned over going through a turn.
3) be mindful of wind gusts, especially going down. No worse feeling than being leaned over 10-15 degrees in a fast turn and a wind gust comes along and wobbles the front wheel.
4) lastly, enjoy the views (if it’s not smoggy). One of my favorite places to ride.
Cheers, and keep it in the big ring ;-)