Take highway 395 south of Mammoth Lakes. Near the green church is Benton Crossing road. Turn left and take Benton Crossing road until you are near the Owens River. If you pass the Owens River campground you've gone too far.
Benton Crossing is located about 10 miles southeast of the town of Mammoth Lakes, in the eastern Sierra. We were lucky in that the entire time we were on vacation, there were daily afternoon thunderstorms. One great place to watch these Sierra thunderstorms is to find a place out by the Owens River. This photo is from a typical afternoon in the eastern Sierra.