Union Falls via Mountain Ash Trail

The ideal time to hike to Union Falls is typically from mid-July through early fall. Before mid-July, the required ford of the Falls River can be swift, cold, and knee-deep, making it quite challenging. Later in the season, water levels are generally lower, and the weather is more stable, offering a more enjoyable experience.

The trail features varied terrain, starting with wooded sections and open clearings. You'll follow Mountain Ash Creek and the Falls River. While mostly flat, there's a notable 600-foot elevation gain on a ridge, particularly on the return trip. Be prepared for two river fords: the Falls River, which can be challenging, and a shallower ford of Proposition Creek. The area around Union Falls can also be muddy and slippery due to spray.

No, dogs are generally not permitted on backcountry trails in Yellowstone National Park, which includes the route to Union Falls. This regulation helps protect wildlife and ensure the safety of all park visitors. Always check the latest Yellowstone National Park pet regulations before your visit.

Yes, since this trail is located within Yellowstone National Park, you will need to pay the park entrance fee. Additionally, if you plan to camp overnight in the backcountry, a backcountry permit is required. Day hikers do not need a specific permit for the hike itself, but park entrance fees apply.

The most common trailhead for Union Falls is located at Grassy Lake Dam. Access to this trailhead is via Grassy Lake Road, which is known for being remote and often rough. Parking is available at the trailhead, but spaces can be limited, especially during peak season. It's advisable to arrive early.

The primary highlight is the impressive Union Falls itself, a 250-265 foot fan-type waterfall where two creeks converge. Another major draw is the geothermally heated Scout Pool (also known as Ouzel Pool), a natural swimming hole perfect for a refreshing dip. The trail also passes through the 'Cascade Corner' of Yellowstone, an area rich with streams and smaller waterfalls.

This trail is considered moderately difficult due to its length (around 15-16.6 miles round trip) and the challenging ford of the Falls River. While the overall elevation gain isn't extreme, the distance and river crossing make it less suitable for young children or beginner hikers. It's best for those with some hiking experience and good physical fitness.

As a backcountry trail in Yellowstone National Park, you are in prime wildlife habitat. Bear activity is possible, so carrying bear spray and knowing how to use it is highly recommended. Be aware of your surroundings, make noise while hiking, and store food properly to avoid attracting animals.

Yes, sections of this route follow the Mountain Ash Creek trail and also pass through parts of the Union Falls trail. While not a major intersection with long-distance routes, these are official trails within the park system that you will encounter.

The most significant challenge is the required ford of the Falls River. It can be swift, cold, and knee-deep, especially before mid-July. An insider tip is to consider hiking later in the summer (mid-July onwards) when water levels are typically lower, making the ford less difficult. Also, be prepared for the 600-foot elevation gain on the return journey, which can feel more strenuous after a long hike.

Given the trail's length and backcountry nature, bring sturdy hiking boots, layers of clothing suitable for changing weather, rain gear, plenty of water, high-energy snacks, a map and compass/GPS, and bear spray. Water shoes or sandals are highly recommended for the river fords. Don't forget a swimsuit if you plan to enjoy the Scout Pool!