There is a hilltop here that is Chert and the Natives used it for arrowheads.

[AnotherDreamWeaver]

A geologist came to our area to check out some soil types and various formations, we mentioned the chert and he wasn't impressed until he saw it. A very well metamorphosed type, coming mostly in a rust red, but yellow and green too. Almost as good as obsidian for tools. He explained how it was ancient sea bed that had been sub-ducted, gone through heat and pressure and then been uplifted. Just South of Ft. Ross is where the San Andreas fault comes ashore again and goes North along the South Fork, then North Fork of the Gualala River. There are very large blocks of stone found around here that came from the Sierra Mountains. This section of the Coast Range is quite a blend of soil types.