About 30 miles south of Big Timber, Montana, the Main Boulder River plunges dramatically over a 100 foot limestone cliff forming Natural Bridge Falls. Although the limestone bridge formation that once spanned the river collapsed in 1988, the Natural Bridge Falls Recreation Area remains a popular destination along the Boulder River Road. Paved paths provide easy access to several overlooks of the falls and Boulder River Canyon. During low water, the river actually cuts through underground channels and bursts out near the base of the limestone cliff. At first sight, this may not seem as impressive as the 100 foot drop seen during high water, but the falls at low water are still a fascinating spectacle and lesson in geology.
After exploring the falls, cross the Boulder River on the sturdy wooden footbridge and continue hiking through Gallatin National Forest along Green Mountain Trail 94. The first part of the trail offers views of the Natural Bridge Falls area which many visitors unfortunately miss the opportunity to see because they never venture beyond the paved paths. After a short climb up and out of the river canyon, the trail brings hikers through open meadows with excellent views of the Boulder River Valley. The path gradually meanders up Green Mountain into thick forest interspersed with small mountain meadows. Watch for elk and deer. As always when hiking in Montana, be bear aware. I observed bear tracks about 2.5 miles up this trail in late April 2010. Eventually, the trail descends into the East Boulder River Valley ending at East Boulder Campground after covering about 5.5 miles. (Some online sources say the trail is 5.5 miles one way, while one of my topographic maps marks the distance as 6 miles.)
Keeping in mind that snowpack levels have been well below average this year in Montana, the Green Mountain Trail was mostly snow free when I visited in late April. A diverse array of wildflowers was out in full force making spring a wonderful time to visit the Natural Bridge Falls Recreation Area.
A note of interest to anglers: only Rainbow and Brook trout are found in the Boulder above Natural Bridge Falls while Brown Trout, Rainbow Trout, and Whitefish are common below the falls.