A great ride, that can be done on your own or as an organized ride is the ride around Lake Tahoe. It's 73 miles with some hills. There isn't much of a shoulder to the road on the east shore. But the scenery is spectacular the whole way. The organized ride is called "The Country's Most Beautiful Ride" (or close to that) and is usually in June, depending on the snow situation.
Another fun organized ride is the Sierra Century, in the Amador County wine country. Just beautiful! This is a wonderfully supported century. One caveat: there is about 8500 feet of climbing during the ride. A lot of it comes in 2 big hills. But it is worth it. This one also takes place in early June.