When seen on a map or aerial photo, the Sutter Buttes appear as a circular array of eroded rocky pinnacles. They are in fact, the remains of an extinct volcano that erupted about 1.5 million years ago. They are considered to be the world's smallest mountain range.
The 40 mile ride is almost completely flat with just a bit of climbing in the first 4-5 miles. On weekends, park in the parking lot of the local high school, on the west side of Acacia street. The ride can be done clockwise or counterclockwise, but there's no particular reason to choose either direction. Very scenic, quiet, low traffic except for the the last few miles on Butte House Road.
Note: There aren't any public restrooms in the area. Stock up in advance and visit facilities in nearby Yuba City/Marysville before you start the ride. Enjoy!