Lake Shasta is closer to Susanville by about an hour I believe, although the diving is inestimably more boring in Shasta.
I don't think there's even a dive shop in, or around, Susanville. At least I haven't heard of one.
No matter how you slice it, it's a long haul to Monterey. I am world-renowned for my high speed driving habits, and it takes me 5 hours to get to Monterey, so it's probabally about 7+ from Susanville.
Give us a jingle and we'll take you and the scooters up to the Lake sometime! Go fly the wall or "somesing".
All the best, James