I've done lots and lots of biking in and around Sacramento and down into the Delta as far as Lodi or so. And although I haven't ridden between Sacramento and Oroville I do know the area, having spent 55 years or so around Sac. Very little elevation gain. The elevation around Oroville is about 200 feet, and you're close to sea level in Tracy/Stockton. Weather probably anywhere from 50's to 60's, possible rain, maybe some fog, maybe nice sunny and cool days. Wind is anybody's guess, depending on if there's a storm in the area or not. Typical wind tunnel effect ("Delta Breeze") through the Carquinez Straights are long gone by that time of year. Routes? Lots of back roads heading up in that direction, bike paths around Sacramento - American River Bike Trail (aka Jedediah Smith Memorial Trail) and Sacramento Northern Bike Trail - and probably in Stockton but they aren't going to stretch too far north out of the cities. Davis is a cool city for bikes but probably out of your way a bit.
100 miles per day is a pretty tall order for a bunch of people who aren't avid cyclists. But it's not impossible, especially if the riders are in good shape. At that rate you'll be there in a day and a half.
Last edited by simplygib; 09-23-12 at 06:40 PM.