When we were there about a year ago, the road was dirt with a washboard surface, but not terrible. We camped at the spaces near the boat landing area, which requires you to go up a short, fairly steep hill past the pit toilet. This is a dead end path, and while there were technically two spaces, our trailer blocked the road so only one space was really accessible. We had to back out for a ways and then were able to turn around in the gravel lot in front of the toilet area. I suggest you look at Google maps satellite photos to see the area. NOt sure if the link will work, but here goes: https://www.google.com/maps/place/Salmon Falls Creek Reservoir/@42.131155,-114.7275504,288m/data=!3m1!1e3!4m5!3m4!1s0x80a9d0f7e5e679b3:0xb863c1f3f8845128!8m2!3d42.1290297!4d-114.7395226

Washboard for about 2 miles. The toilet is visible to the left of the lake up a hill which is where you camp.

There are a few road intersections where we saw people camp driving into the site. Road was good but you'd need to be careful and drive slow if driving a car. There is only one site near the toilet that has a firepit and picnic table, but you could camp right near the lake if it is taken.