I came across a thread of info about waterfalls in the western USA, and decided that I needed to plan a hiking trip solely focused on seeing more waterfalls that are best seen as part of an amazing hike!
If you have any more to join, please leave them in the comments; I'd be happy to add more to the list so it can become a reference of sorts!!
You can hike to see both the Upper and Lower Yosemite Falls; be aware that they dry up later in the season! The Mist Trail to see Vernal and Nevada falls is one of the most popular hikes in the Valley, so go for it! Find out more about this potentially dangerous trail here.
Columbia River Gorge area in Oregon
The best hike will take you to Multnomah Falls, which is the tallest waterfall in Oregon. There are also a ton of other waterfalls to see in the area, so check out this list of 5 amazing hikes to do in the Gorge!
Silver Falls State Park
Ten Falls Canyon Trail is said to be pretty amazing: family friendly AND you get to see 10! waterfalls throughout the hike.
Punchbowl Falls, Oregon
Punchbowl Falls is pretty cool, and it's an easy 3.8 mile round trip hike to see it! Check out out the trail and you can even add on some more waterfalls if you're up for a longer trip.
Glacier National Park in Montana
Going to see both Virginia Falls and St Mary's Falls in one hike is doable, and you can see amazing views. While most of the hike will be in the woods, the waterfalls themselves are beautiful and you can practically stand underneath Virginia Falls. Hikespeak has some awesome instructions for hiking there!
Lower Yellowstone Falls in Yellowstone National Park
The trail to the top of the Falls (3/4 of a mile roundtrip, but steep with many switchbacks) is a must, as the experience of standing atop the Falls is one of the most breath-taking experiences in the entire Park.
Pacific at McWay Cove in Big Sur, California
McWay Falls are pretty amazing. They're near the road and an easy hike, so why not go them? Sure, compared to the waterfalls you can see a few hours away in Yosemite National Park, they may be somewhat underwhelming.
Olympic Peninsula in Washington
There is an amazing map of all the different waterfall trails through the region provided by Olympic Peninsula Waterfall Trail. And boy, are there a lot of waterfalls! I won't try to choose for you. Explore them yourself.