Skagg's Spring just came up on my clubs chat list and advice on water sources was given:

"You will want to fill your bottles at the Lake Sonoma Visitor's Center... it's a long ride to the next water stop (more in time than miles). The next water is at the YMCA Camp... you'll know it when you get there. There is water on the deck of the main building. When you get to Stewarts Point there is a brown building on the left just before you get to Hwy 1 with a water spigot on the left side of the building. Traveling south on 1 there are some campgrounds and a couple of convenience stores before the Ft Ross turnoff."

Anybody considering this ride should probably note this on the map now that were heading for summer.