Union Falls is a veiling horsetail waterfall of about 147 feet on Mountain Ash Creek in the Bechler region of Yellowstone National Park, Wyoming, the park's wet, waterfall-rich southwest corner. It fans out wide over a cliff where a side stream joins the creek right at the brink, and reaching it takes a long day or an overnight trip with a cold river ford.
The falls
Mountain Ash Creek spreads into a broad white fan as it drops, with a tributary pouring in at the very lip. A lidar measurement puts the drop at just over 145 feet; earlier surveys listed 260 feet, and 250 feet is still widely quoted. The falls face west, so the afternoon light is best for photos.
Getting there
The usual start is the Cascade Creek trailhead below the Grassy Lake Reservoir dam, about 10 miles west of Flagg Ranch on the unpaved Grassy Lake Road; the last stretch down to the parking area is steep and rough, and the road can be closed or impassable into June. From there it is about 8 miles each way, 14 to 16 miles round trip by various measurements, with 1,700 to 2,000 feet of climbing. About 1.5 miles in, the trail fords the Falls River, some 40 feet wide, knee-deep, swift and cold; smaller creeks are crossed on logs. Longer routes start at Fish Lake or the Bechler Ranger Station.
Day hikes need no permit; camping requires a backcountry permit, $5 per person per night plus a $10 reservation fee. Yellowstone admission is $35 per vehicle for seven days, plus $100 per person for non-US residents aged 16 and older unless they hold an Annual or America the Beautiful Pass.
When to go
The Falls River ford can be impassable in June and early July, so mid-July through September is the usual season. Mosquitoes are thick in Bechler in early summer; bring repellent and a head net.
On site
A short side trail leads to Scout Pool, also called Ouzel Pool, a clear pool about 20 feet across and 7 feet deep warmed by a spring and fed by a small waterfall. The current from the inflowing creek is strong, and a diving injury there once required a helicopter evacuation; keep your head above water and stay out of thermal pools. Carry bear spray, hike in a group, and stay 100 yards from bears. Dogs are not allowed on trails.
History and name
Members of the Arnold Hague geological survey named the falls in the 1880s; geologist Joseph Iddings noted that a tributary joins Mountain Ash Creek at the very brink, "thus Union Falls."
Nearby
Early Morning Falls is about 0.5 mile away, and Morning Falls and Riverwalk Falls are each about 1.3 miles.
Distances are straight-line.