Chico Velo puts on a terrific series of centuries rides, all close to you. The winter rides usually have same day registration so you can look at the weather. The Rice Valley Tandem rally goes around the Sutter Buttes when the cranes are there and lots of singles riders are out sucking wheel. So, don't feel shy. As close as you are to Chico, I highly recommend one of the Wildflower routes in April, though this year there was rain in the mountains and last year was a record high.
The 2006 info isn't up yet, but you can still download the maps.
http://www.chicovelo.org/centurydates05.html
PS - the week in the Canyonlands was by royal command as issued by Princess Zippy. :)