You can do this as out and back or as a loop. To make a ~6 mile loop, take the fork to the right that goes past the gate about 2.5 miles in. Larger loops are possible with later turnoffs.

Heading west from the Salmon Falls bridge, this trail winds along the side of the river at various elevations -- high above at first, then down to river level later. 8.5 miles one way to the peninsula campground, and continues on past that. Along the way there's plenty of nice river views. There's also some forks you can take along the way for variety, I believe they all rejoin the main trail eventually but haven't verified.

Significant portions of the trail are exposed to the sun, so not much fun in summer.

The early part of the trail can get a bit busy at popular times, with mountain bikers being especially common on the narrow trail. Be alert and don't have your ear buds in.

$10 paid parking lot, or gravel parking across the bridge or wherever you fill a gravel pullout without a no parking sign (free parking likely fills up early on weekends).

According to https://getoffyourgass.com/darrington-2/ "Levi Darrington was a pioneer of 1860 who had a 780 acre ranch in this area after he gave up mining and became a butcher."

When the water is low in the summer, you can combine Darrington with Sweetwater by crossing Hidden Bridge to make a ~6 mile loop. At low water you may also find some interesting historical structures: insuremekevin.com/hiking-a...-lake-in-el-dorado-county/