Ruck-A-Chucky Rapids Trail is a 6.3 mile lightly trafficked out and back trail located near Foresthill, CA that features a river and is rated as moderate. The trail is primarily used for hiking and trail running and is accessible year-round.
Make the drive down to the campground area. We made the mistake of deciding to hike down (and back up) the road which isn't that nice of a hike. Once down there though its a beautiful area.
This is a beautiful trail along the Middle fork of the American River. It is part of the Western States trail. You park by the campground or a little further up in the fee areas. From there it's a dirt road you follow for about a mile to the WST entrance gate. You see the gorgeous Rapids before this tho. It's super hot in these canyons in the summer with temps that reach 100+ easily. Bring plenty of water and sunscreen. From the WST entrance, it's 4 miles to Fords Bar.
Driver's Flat Road is pretty steep, I would recommend at least an SUV, although it is usually possible in a car. This is part of the Western States Trail and leads out of Ruck-A-Chucky campground (a fee area) following the river, although you will have to walk a few miles before it actually drops down to the water at the first sharp bend, which is as far as I've ever been. Up to that point it's a fair dirt road, afterwards it turns into a slightly overgrown foot trail. Apparently you can follow it all the way to Foresthill if you want - about 15 miles away, and it doesn't appear to connect to any other trails, so consider this an out-and-back. The best time to go is any time but summer, it gets hot and the first stretch of trail is on a south-facing slope that will be covered in dry grass, winter and spring are best if the road is open. Although not really needed for this one; you can pick up a free, non-topo trail map at park HQ on highway 49, there's also a big map posted at Ruck-A-Chucky.
Pretty gnarly to get to, but easy once you get there. Hike is the best just 1 mile in at the falls which are down a tougher trail to navigate (no kids, dogs or the like). The rest winds along the river for the most part.