What Murph said though if you do the Annapolis loop CCW it’s not as steep a climb up to the reservation.
Another loop is Old Stage out of Gualala. Take it north as far as you want. Make it to pt arena and grab a coffee or drop down Fish Rock or Iverson and head back soyth on the coast.
If you’re looking for a nice dirt road, head south into Salt Pt and climb Kruse Ranch Rd. Take a left at Sea View and climb up Hauser Bridge to Tin Barn. Left there and your back into the reservation from the south.
Stump Beach trail just past Kruse ranch is a great road bikeable (when dry) climb up most of Kruse. Not sure if it’s less than 10%, but it’s amaze.
Last, if you can swing a pick up when heading home ride one of the last two option up to Sea View, but turn right and take the ridge all the way to the top of Meyers Grade. Drop to the ocean and into Jenner for a stop at Cafe Aquatica.
I’m happy to send Strava of all these routes when I’m back at a computer. Let me know if you are looking for longer. You could do King Ridge loop too
1T