I'm finally realizing that my Zumo 550 GPS isn't good enough to help me find a way through the dirt roads up in the Sierras. On Saturday when attempting to ride the dirt roads between Nevada City and Downieville, we got lost a few times and it was only because one rider had a National Geographic Tahoe National Forest map that we figured out an unpaved route out of there that wouldn't also take us way out of our way. So I've figured out that National Geographic maps 804, 805, and 806 seem to cover areas that I'm interested in "getting lost" in on a motorcycle. The detail is about right for choosing roads. The problem I have is that I can't find a "big picture" map that shows where the more detailed ones are located. The National Geographic site tends to dump all maps together and it's hard enough to even narrow them down to California. Short of going through the numbers using Google: "National Geographic Maps 800", 801, 802, and so on, is there a better way to find out what all is available? Ultimately I would like that level of maps for all of the Sierras north of Yosemite up to Mt. Lassen. I already have the Butler Maps Northern California road map, and the regional maps from AAA. Suggestions?