Ponytail Falls is located above Horsetail Falls on Trail 438 which loops up from Horsetail falls and crosses over to the next canyon west which contains Oneonta Falls and Gorge where it joins Trail 424. Walking behind waterfalls is always popular, and in the case of Ponytail Falls, the official Forest Service trail passes through the dark recess under the basalt cliff.
This photo was also taken from the trail. From this popular vantage point, the falls appears to gush straight out of the cliff face and forms this graceful arched shape.