Here is a GPX track log for this hike right click to save it.
South Mountain is the southernmost mountain in the Olympics. From the top at 3,070 elevation you get an undiminshed 360 degree view. 
Wow! What a view! You get a slight feeling of vertigo up there as every thing drops straight down from the tiny summit. The views start just .5 mile from the trail head and keep getting better until you reach the top. I'm really impressed with the view.
The view is well worth the effort to get up there. It Would be a real waste of effort to do this hike on a cloudy day, wait until it is clear so you can see the view.
You can look north and see the snow capped Olympics, Look east and see the cascades including Rainer, St. Helens and maybe even Hood.
To the south you look down on the Chehalis Valley. To the west you can see a band of blue that is grays harbor.
You can get to the "trailhead" in a car, the 800 line is like a dirt superhighway, but if you have a truck or other high clearance vehicle bring it. It was easy going for my jeep even at 45MPH.
To get to the trail head take the Shelton Matlock exit off highway 101 and head for Matlock. After a few miles you will see a sawmill on the right. A bit past the sawmill on the right is the entrance to the 800 line. Follow the 800 line until you reach the intersection with the 820 road and turn right. Park near the gate and start walking.
If you're really lucky like I was today the gate will be open and you can drive all the way to the top. But beware you could get locked in!
This is a great winter hike! 7.75 miles round trip with a nice gentle grade. There was snow on the top when I placed my terracache there in January but there was no snow on the top today.
A jogging stroller or bicycle would do fine on this road in the summer.
If you manage to find a way to drive up there the terrian rating will be much lower but you will for sure need vehicle with VERY good brakes.
There is a warning sign about RF near the cache but I have been assured by users of the repeater that this is not something to worry about unless you actually try to climb up the repeater tower.