The South Fork of the Smith has several wonderful options for paddling and most people choose paddle between Steven Memorial Bridge and Jed Smith Redwoods State Park. You can do this as a full day of Class II-V rapids or break it up into shorter sections depending the type of rapids and length you're looking for. The entire stretch has a road nearby.
The South Fork is probably best known among paddlers for its Class IV/V gorge downstream of Craig's Beach. The rapid are Class IV or V depending on river levels and how you rate rapids. This a short section of challenging and fun rapid in a narrow gorge that would be tough to hike out of if you're having problems.
Mile 0: Put-in at Steven Memorial Bridge on the South Fork Road.
Mile 4.1: Boulder Creek Rapid (III+) is the first challenging rapid. It can be scouted at river level or from the road on your drive up to put-in.
Mile 5.5: Sand Camp River Access is a great place to put-in or take-out if you want to do a shorter run.
Mile 8.9: Coon Creek Rapid (III+) begins just after Coon Creek joins the Smith River from the right.
Mile 11.4: Surprise (IV) is a steep drop that can flip rafts. It can be scouted by catching a medium sized eddy on the right just above the rapid.
Mile 11.8: Craig's Creek enters from the right side. The take-out trail above the South Fork Gorge at Craig's Beach is just downstream.
Mile 12: Craig's Beach has a steep singletrack trail that can be use for river access. Carrying your boats up the hill here will be a test of raw strength and teamwork. You can continue downstream for the Class IV-V (depending on flows) South Fork Gorge that is 1.7 miles and 50 fpm.
Mile 12.6: Slalom Course (III) is a good warm up rapid before entering the gorge.
Mile 12.7: Gorge Entrance (IV) is the first rapid in the gorge and will give you a sense of what the rapids will be like downstream.
Mile 12.8: Good Luck! (IV+/V) is a tricky rapid that can be scouted from either side of the river.
Mile 12.85: The Boof (IV+) can be scouted from the left. There are several lines here, but at moderate flows most kayakers opt for a boof on the left.
Mile 13: The Slot (IV) is a narrow rapid with multiple channels depending on flows.
Mile 13.1: Final Rapid (IV) is the last rapid in the gorge and can be scouted from the right. It has a steep ramp that sends you into a rock shelf on the left side of the river.
Mile 13.7: River Access at Second Bridge. It's a steep walk up a narrow trail that's fine with kayaks but can be challenging with rafts. From the top of the bridge it's a short walk to Forks Boat Ramp. If you have rafts you may want to consider paddling downstream to Jed Smith Redwoods State Park.
Mile 16.1: Jed Smith Redwoods State Park is a beautiful place to take-out and camp.