There is actually a trail head for Mystery Lake if you continue down into the valley from Loon Creek Summit. Continue along the road, it gets very rough but is passable make sure you have a high clearance vehicle and 4 wheel drive, this road is notorious for flat tires and busted oil pans. After descending into the valley continue along the road, it's a little bit of a drive but on the left hand side of the road you will see Mystery Creek coming out of the woods. There is a parking/camping area off to the side. The trail heads up following the creek most of the way, there is a great waterfall overlook about half way up but be careful if you decide to venture out for a better view because it is covered in loose rock and is a long drop down. The trail can be hard to follow at times and is very steep in sections (hand over foot). About two miles up the trail you crest a ridge and come down into the lower lake, great camping and fishing here. The woods around the lower lake are dense enough to provide shelter from the elements. Looking South West across the lake (facing The General) you can make your way around the left (East) side fairly easily where you'll find Mystery Creek, you can follow the creek to the upper lake. There is a "trail" it is a very steep and tough way up but it is very worth while. Once you crest this ridge, the view of Upper Mystery Lake with The General looming the the background is spectacular. From here you can make your way around the right (West) side of the lake to a ridge leading to The General's summit. I personally have only made it half way up this ridge before having to turn back as night fell, but from where I got to, it seemed like a very viable route to the top. Going this way, I would suggest making it a three day trip. The hike up from the parking area to the upper lake is a tough one, about three hours of brutal uphill gaining about 700 vertical meters and roughly 3.6 km long (based on Google Earth). Either lake makes for great camping and if you're a fisherman, bring along a float tube because there is some great fishing at both lakes. All in all, this is a very remote and beautiful area to explore.
Parking lot lat/long: 44 30,08N 114 46,33W
Yes sir, I know the spot. I drive past that on the way up elk hunting every fall. Thank you.
FYI the elevation of The General is 10,329 ft. and not 10,341 ft. as posted here. This is what is marked on the USGS topo and other sources I have encountered.