Had a lovely hike from the Oneonta Gorge trailhead (just west of the Tunnel), up and over the bridge and down behind Upper Horsetail Falls to come out on Horsetail Falls. There is a beautiful viewpoint between the Oneonta bridge and Upper Horsetail Falls that's work the walk all by itself. It's also exceedingly cool that the trail goes behind the upper falls, with a nice view down the creek out to the Columbia. There's a bit of steep involved, but the payoff is a beautiful hike, and all downhill on the way out ;).
About three miles total for the loop, which will put you back on the scenic highway about 1/4 mile from the starting trailhead - normally I would warn you off against walking along the highway, but there is a large shoulder through this stretch.
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