I approached State Line Peak using Highway 395. The small town of Doyle is about 45 miles north of Reno and about 45 miles south of Susanville. It has a signed turnoff from Highway 395. In fact there are at least 2 exits on either side of Doyle and there is a loop road that connects the 2 exits through Doyle. About .75 from either exit on the south side of Doyle on the loop road you will find a road that goes east and immediately crosses the railroad tracks.
From the railroad tracks note your trip odometer and follow this road as it goes left then right, crosses the Long Valley Creek and then turns left again. All this within about .75 mile from the railroad tracks. Just after this last left turn, turn right on the first road. This is Homestead Ranch Road and it goes southeast along the base of the Fort Sage Mountains. So far all these roads are good roads and any 2WD vehicle is ok.
Stay on this road for 5.9 miles from the railroad tracks, where a lesser road goes left up a canyon into the Fort Sage Mountains. This lesser road follows a creek bed for about a mile and then meanders around the mountains while it gains elevation. At 8.0 miles and elevation 5,760, the good part of the lesser road ends, but 4WD continues. I kept going to mile 8.5 and elevation 5,880 where I reached a boulder blocking obstacle on the road. I stopped here and hiked from this spot. There were other obstacles within a half mile ahead that would have stopped my anyway.
This route is not technical from the west. The route is fairly simple once you arrive at the trailhead. The trailhead is anywhere you stop along the road up the canyon. After you park, continue up the canyon. You will reach the first saddle about .5 mile from where I parked and this is where the 4WD road ends at about 6,100 ft. The rocky trail turns left (north) here and goes up to another saddle at about 6,400 ft. This saddle is between points 6561 and 6946 on the topo. There are great rounded light colored rock formations to the west side of the trail as you hike up to this saddle.
Once at this saddle, you are on the west ridge of State Line Peak. Leave the trail and climb up to the top of the ridge on your right. It is kind of steep at first, but once on top you will be able to see the west ridge all the way to the summit. There are some large rocky outcroppings along the ridge and I stayed left (north) of all these following livestock trails or just open grassy slopes. Follow this ridge all the way to the summit where there are a couple buildings and small communication towers.
Total hike is 5.5 miles, gained 2,110 ft, and takes 3 to 4 hours.
The 10 essentials are always required. There is no water on the trail, so take all you need. A GPS may be handy depending on your navigation skills.