Union Falls had to have been my favorite waterfall in Yellowstone National Park besides the powerful Lower Falls of the Yellowstone River. It had been frequently described as the most beautiful waterfall in Yellowstone National Park, and it wasn't difficult to imagine why as you can see from the photo at the top of this page. While Lower Falls had the obvious power and size residing within the impossibly beautiful Grand Canyon of the Yellowstone River, Union Falls possessed a more delicate and graceful quality punctuated by its uniqueness and size. The falls' 250-260ft drop (said to be the second highest permanent waterfall behind Lower Falls) with a width that was seemingly at least as wide as it was tall made it an imposing sight. Yet its teepee or curtain shape (resulting from the union of Mountain Ash and an unnamed creek) ensured that there was no other waterfall quite like this. As if that wasn't enough, I was even able to take a dip in a geothermally heated lukewarm swimming hole beneath a separate waterfall at the Ouzel Pool (also referred to as Scout Pool), which was a short side excursion for a little play and relaxation. Indeed, Union Falls seemed to have checked all the boxes in terms of all the things you'd want in a waterfall, and thus it earned a spot on our Top 10 Waterfalls of the United States List!
With so much going for Union Falls, there had to be a catch, right? Well, it turned out that in order to access Union Falls, I had to go on a lengthy hike that was a minimum of 15 miles round trip and included an intimidating ford of the Falls River as well as a nearly 1000ft of net elevation gain that involved quite a few undulations. Since I added the side excursion to the Ouzel Pool, that pretty much extended my hike by almost another mile. The trails also passed through areas frequented by grizzly bears so being bear aware in addition to being physically and mentally prepared was a must in this backcountry adventure. Julie and I learned the hard way back in June 2004 that it was not a waterfall that you could just show up without the necessary preparations and conditions. Back then, we went as far as the Falls River ford when the swift currents and depth of the river aborted that attempt. This waterfall had haunted me ever since that failed attempt, and it wasn't until a subsequent visit to Yellowstone in August 2017 when all the precautions and lessons learned finally paid off.
On that second attempt, I should note that I took a calculated risk doing this hike alone as it's recommended to hike in groups of at least three people to minimize the likelihood of having a close encounter with a grizzly bear (and thus a higher potential of an attack). Although it didn't logistically work out for me to start this trail in a group (it was too long and difficult for Julie and Tahia to do), I knew that doing this hike on a Saturday meant there would be more people on the trails, and my suspicion played out as I wound up hiking with a group that just so happened to be going at a similar pace as I was. I also carried bear spray with me just in case, but I left the bear bells behind as grizzlies have learned to treat them as dinner bells as they've associated that sound with food stored in packs. In addition to being bear aware, I also brought a pair of trekking poles, which were helpful in maintaining balance on the intimidating Falls River ford as well as a change of shoes (preferably river shoes or sandals) so the hiking boots wouldn't get ruined. Then, of course, I had gotten an early start to ensure that I'd be back before dark as I was on the trail by 7:30am and it took me over 10 hours to complete. Finally, if all this preparation might make it seem like too much trouble, I realized after the fact that there were plenty of groups on horseback so it was possible join tour operators offering such excursions (making it possible to bring kids).
Logistically speaking, there were actually a few different ways to visit Union Falls, and each one had differing lengths and degrees of difficulty. On this page, I'm describing the shortest route, which began from the Grassy Lake Trailhead (see directions below). There were also trailheads at Cascade Creek (the same trailhead for Terraced Falls) as well as Cave Falls near the Bechler Ranger Station accessed from the Cave Falls Road, which crossed into Yellowstone National Park across the Idaho border. These longer options make the round trip hiking distances (not including Ouzel Pool) 15.6 miles and 23 miles, respectively.
From the fairly spacious Grassy Lake Trailhead, which was at the bottom of the dam holding up the Grassy Lake Reservoir, the trail started from the west end of the clearing. After going past a bridge traversing some kind of spillway then passing by a sign indicating that I was entering Yellowstone National Park, the trail then traversed a wooded area that alternated between being densely packed with thin trees and pockets of clearings. Along the trail, I noticed some berries, which was an indicator that bears would forage here. After a little over a mile, the trail then was joined by the Cascade Creek Trail on the left. This junction was noteworthy because it could be confusing on the return hike which fork to take. For roughly the next 400-500ft beyond this trail junction, the trail descended as the sounds of the Falls River grew louder and would eventually meet the Falls River at about 1.2 miles from the trailhead. This would be the time change into shoes that could get wet while hopefully the mosquitos wouldn't be too bad as we were sitting ducks for them.
Although the routing of the trail seemed to suggest crossing the Falls River via a small grassy island just past the middle of the wide river, I was with a group that figured out that it was a bit less deep if we made our crossing not far to the left of that island. With the aid of wooden sticks or trekking poles, we managed to keep our balance, especially through the deepest part (which got to about thigh deep just past the island) while traversing diagonally facing downstream (so you'd fall forward if such a calamity happened) before reaching the other side. Surprisingly, the Falls River was not as cold as mountains rivers would typically be, which suggested that there were plenty of geothermal tributaries and sources feeding the Falls River to warm it up to the extent that the morning crossing wasn't as painfully cold as anticipated. Once on the other side, we could change shoes to resume the hike (I was able to continue straight away since I was wearing Keens though I did experience a problem with chafing later on).
Beyond the Falls River ford, the trail then made a moderate climb for at least 200ft or so going past a junction with the Pitchstone Plateau Trail, then following along more wooded terrain as the climb eventually leveled out. The trail would persist this way for nearly the next 1.5 miles as I then descended towards a seasonal creek with standing water and fallen logs that I was able to use to keep from getting wet. Beyond this obstacle, the trail then made a short climb before leveling out again revealing hints of mountains and plateaus in the distance as well as the trail surface becoming rockier in spots. The flat part didn't last long however, as I then found myself making a steeper and more prolonged descent towards Proposition Creek (which was about 2 miles from the seasonal creek crossing or 3.5 miles from the Falls River ford). This long descent would be a pretty tiring climb on the return hike (as about 600ft of the nearly 1000ft elevation change was in this stretch) so I braced myself for this mentally.
Unlike the Falls River ford, the crossing at Proposition Creek was more like ankle deep, and it was bitterly cold (more like what you'd expect the water temperatures to be on a typical mountain stream). Depending on its depth, some time would have to be spent changing shoes again. Beyond the crossing of Proposition Creek, the trail meandered through extensive patches of lush low-lying bush and shrub (many of which grew berries and wildflowers) surrounded by tall trees as it continued its descent towards Mountain Ash Creek. I'd have to say that this seemingly more moist part of the trail was a haven for mosquitos, which seemed to be pretty fierce during my visit so I tried to keep moving while also re-applying DEET. Finally after about another mile from the Proposition Creek crossing, the trail joined the Union Falls Trail, which ran alongside the fairly sizeable Mountain Ash Creek. I turned right at the junction to follow along the creek upstream.
The Union Falls Trail seemed to be pretty wide and well-used compared to the Mountain Ash Creek Trail that I was just on. After going through some more low-lying shrubs with berries (so this was definitely a spot where bears would forage), I then encountered a part where the trail disappeared into the Mountain Ash Creek at about 0.6 miles from the last trail junction. Fortunately, I didn't have to ford this large creek as there was a sign pointing to a narrow single-log footbridge. So after taking that footbridge, I then continued following the trail before encountering a ranger station some 500ft later. As I continued hiking beyond this station (noting that there were more signs indicating backcountry camping spots), the trail had more sand and horse poop as it was clear that this trail saw more than its share of stock. Eventually at nearly another mile beyond the ranger station (or 1.5 miles beyond the Mountain Ash Creek footbridge), I reached another trail junction.
At this junction, there was a fairly large corral accompanied by a sign saying stock use ended there. I first took the right fork at the junction, which then proceeded to climb another 200ft on a narrower path. Eventually, after another 1/2-mile from the trail junction at the corral, the official trail terminated on a ridge overlooking the impressive Union Falls through a couple of clearings in the vegetation. At this point, I had hiked about 7.5 miles from the Grassy Lake Trailhead.
As of my August 2017 visit, this west-facing waterfall still produced enough spray to be felt even on the ridge I was on. While I first showed up in the late morning when the sun was right on top of the falls, I would later come back for more reasonable lighting in the early afternoon. I also noticed that there was a steep scramble leading to a moist and muddy trail that eventually led down to the base of Union Falls. Although I didn't do this, I saw plenty of people that did so it didn't seem all that bad to do it (and it made me wonder if I regretted not doing it). Anyways, after having my fill of this spot (which was perfect for a picnic lunch), I then descended back down to the corral where I then headed onto the other fork. By the time I got back there, I saw horses parked at the corral as well as a handful of more people (including kids) on the trails, which made me realize that it might have been possible to bring Julie and Tahia here with a little more planning and willingness to spend more money.
Nonetheless, on the other spur trail, it continued for the next 0.3-0.5 miles or so towards what the topographic maps had labeled as "Falls". Well, towards the end of this trail, I approached an attractive small waterfall with a plunge pool that had a nice deep blue color to it. There were a trio of people here doing cliff jumps and swims, and there were some rock cairns set up to indicate the end of the short trail. It appeared that the trail kept going, but signage here said that this was the Ouzel Pool Restoration Area (by the way, this sign revealed to me the name of this place) and so I didn't bother to pursue those trails any further.
Contrasting the physical exertion and amount of time spent hiking, this opportunity to dip at the Ouzel Pool was refreshing. It was also lukewarm as the stream must have had geothermal sources and springs feeding it further upstream. Over the next few minutes as more and more people started showing up, this place then took on a more festive (almost party-like) scene as people took turns doing cliff jumps and some kids were enjoying the water in some calmer spots further downstream. After having my fill of this falls, this would be the turnaround point and the start of the long return hike to the trailhead. I actually extended my hike by going back to Union Falls to take some more pictures of the falls in better afternoon lighting. If I had to be more efficient about my visit, I would have gone to this pool first and then go to the Union Falls later before starting the return hike.
On the return hike, I noticed a lot more stock groups going the other way (further attesting to the relative popularity of this backcountry adventure though there was no tourist crush you'd get by Yellowstone's main roads) as well as a few dozen more hikers. Given their late starts, I'd imagine most of them were backcountry camping. Anyways, as expected, the hike went pretty swiftly with the exception of the long ascent that began on the Mountain Ash Creek Trail junction and really got steeper beyond the Proposition Creek crossing. This was where I caught up to the group of hikers I encountered throughout the day, who had gotten an early start than me on the return. On the Falls River ford, the water seemed to have gotten slightly deeper and more swift (as I'm sure more snow that was still around upstream had melted in the heat of the mid-Summer day) so again the hiking sticks and the slightly diagonal downstream trajectory while facing downstream were helpful. I then kept left at the trail junction with the Cascade Creek Trail, which could be potentially confusing if one forgot which trailhead he or she parked at. Eventually after 10 hours away from the car, I finally returned to the Grassy Lake Trailhead to conclude this epic hike. Though the end couldn't have come soon enough as my hiking 16 miles in Keens also managed to chafe both my feet so they were bleeding and definitely needed the breathing room.
Although it extended the Union Falls hike by about another mile, it was worth checking out the Ouzel Pool, which had lukewarm water and a short 10ft waterfall to boot!
Although the Union Falls hike was within the Yellowstone National Park boundaries, it felt like the attractions of the Grand Tetons were closer than Yellowstone's more famous spots
Further to the northeast of the Bechler Backcountry was the vast Yellowstone Lake, which was said to be tilting in one direction due to the bulge of magma beneath the Yellowstone Supervolcano
To the north of the Bechler Backcountry and the west of Yellowstone Lake was the Upper Geyser Basin, which was famous for predictable geysers like Old Faithful
You know you're getting an early start when you see the sun rise. This was from the Grassy Lake Road as I was driving towards the trailhead
Looking at the surface of the Grassy Lake Road
Looking over the dam holding up Grassy Lake Reservoir
This was the start of the steep and narrow spur road descending to the Grassy Lake Trailhead
At the fairly spacious parking area at the Grassy Lake Trailhead
Crossing over the spillway creek beneath the Grassy Lake Dam
Entering Yellowstone National Park
Hiking through the forested terrain of the first mile of the hike
Berries growing along the trail so I knew that bears would forage around this area
This was the trail junction between the Mountain Ash Creek Trail and the Cascade Creek Trail. It was straightforward in the morning which way to go, but it could be potentially confusing on the return hike. In my case, I would keep left to return to the Grassy Lake Trailhead
Facing the ford of the Falls River as the trail disappeared right into it
One guy from the hiking group took the lead as he was the tallest of the bunch so he was better able to scout out the easiest or most shallow approach to the other side
The rest of the hiking group making their ford of the Falls River
Beyond the Falls River Ford, the Mountain Ash Creek Trail made a brief climb
Towards the top of the climb, the scenery turned to lightly wooded, which was helpful in that I had more visibility in case of the odd bear encounter
This was the crossing of the seasonal creek, which was standing water during my August 2017 visit. The logs there helped me keep my feet dry
This scat had berries in it, which made me believe it could have belonged to a bear. But its small size made me realize that it might have belonged to a cub
The backpackers were the first people besides the hiking group fording the Falls River with me that I saw on the trail
The Mountain Ash Creek then began a pretty lengthy 600ft descent towards Proposition Creek
This was the crossing of Proposition Creek, which was very cold. At least it was only ankle deep and was nowhere near as intimidating as the Falls River Ford
Beyond Proposition Creek, the Mountain Ash Creek Trail descended through an extensive patch of low-lying shrubs full of wildflowers and berries (as well as mosquitos)
At the very bottom of the descent was this trail junction with the Union Falls Trail
The Union Falls Trail now followed along the Mountain Ash Creek in the upstream direction
This ominous sign warned of the likelihood of encountering bear, further reinforcing the need to be aware of the surroundings and make as much noise as possible
If not for this sign, I very easily could have missed the footbridge traversing Mountain Ash Creek
Looking back towards the bridge traversing Mountain Ash Creek
I believe this pretty large paw print belonged to a grizzly bear
This was the Union Falls Ranger Station
Following along the sandy trail, which was pounded by stock
This was the corral at the trail fork where the left fork went to Ouzel Pool and the right fork climbed up to the overlook of Union Falls
The narrow ascending trail leading up to Union Falls
Finally arriving at the overlook for Union Falls
Even though Union Falls was deep in the Bechler Backcountry, it seemed as if it wasn't that often that I would have the falls to myself. Still, it didn't feel crowded
Some people were making the steep descent to access the base of Union Falls
If you look very carefully in this picture, there was a white dot on the lower left just behind or next to Union Falls' base. That was a person, which gave you an idea of how large this waterfall was!
On the spur trail leading to the Ouzel Pool
Approaching the Ouzel Pool
It was quite the fun and festive scene at the Ouzel Pool
On the long and strenuous 600ft ascent after crossing back over Proposition Creek to ascend the Pitchstone Plateau
Catching up to one of the hikers who was struggling with this climb
Looking back at a group of hikers going across the seasonal stream while balancing on the logs to stay dry
Back at the Falls River Ford, where another trio of hikers went right past me and right into the river
Looking back at some rapids and cascades on the Falls River, which underscored how swiftly the river was moving at the ford
The final ascent beyond the Falls River and back up to the Grassy Lake Trailhead
Ironically, this spillway was a welcome sight as it meant I had returned to the Grassy Lake Trailhead and I could finally take off the Keens taht had chafed my feet to the point it was bleeding and stinging
The adventure wasn't over yet as I still had to drive up this rugged road to regain the Grassy Lake Road. The key for me was to gain enough momentum to keep going uphill and keep that momentum or else I'd lose traction and have to back up and start again
On the home stretch along the Grassy Lake Road as I was headed back to Flagg Ranch to rejoin Julie and Tahia for dinner
The Grassy Lake Trailhead for Union Falls was at the base of the Grassy Lake Reservoir, which itself was about 11 miles (about 45-60 minutes drive) west of Flagg Ranch along the unpaved Grassy Lake Road (it became unpaved after the bridge over Polecat Creek). The road had a few rough patches with potholes and some water-damaged ruts, but it was otherwise doable by passenger vehicles. Once the road descended to the Grassy Lake Reservoir, that was where there was a spur road to the right just before crossing the dam. That road was very rough and steep, and a high clearance vehicle would definitely be necessary there. So if you have a car that can't handle it, then it would be best to park off to the side at the top of that road, then walk the quarter-mile to the parking area and trailhead below.
For some context, Flagg Ranch was about 2.5 miles south of the South Entrance to Yellowstone National Park, 55 miles (75 minutes drive) north of Jackson, and 72 miles (under 2 hours drive) southeast of West Yellowstone, Montana. While Flagg Ranch was also a mere 48 miles (over 2 hours drive) east of Ashton, Idaho, it was on the Grassy Lake Road (also called the Reclamation Road), which was said to be pretty rough the closer to the Idaho border you go. I've never taken the Grassy Lake Road that far before so I can't say much more about the road conditions.
For additional geographical context, West Yellowstone, Montana was 58 miles (at least 90 minutes drive) south of Gardiner, Montana, 90 miles (over 90 minutes drive) south of Bozeman, Montana, 108 miles (under 2 hours drive) north of Idaho Falls, Idaho, and 321 miles (about 4.5 hours drive) north of Salt Lake City, Utah.
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