American River Whitewater River Rafting Tour. Get ready for the adventure of a lifetime. Spend the morning on the South Fork of the American River, through 8 miles of Class III river rafting fun. In the afternoon, take time to relax or play volleyball, even take a stroll down to James Marshall State Park, site of California's Gold Rush beginning in 1848. This fun-packed day includes the return trip from San Francisco, a full lunch and the whole morning of rafting.