Periodic Spring in Star Valley: Wyoming’s Roaring, Start-and-Stop Waterfall

It starts with silence.

Still forest. Quiet rock face. Just the sound of wind through pines.

And then… a low rumble.

The ground almost seems to vibrate as water begins rushing from the cliff wall, building from nothing into a roaring cascade in seconds.

The first time you hear it, it’s almost shocking. Slightly terrifying. Completely mesmerizing. Welcome to the Periodic Spring, the world’s largest intermittent spring, tucked into the mountains above Star Valley.

Trail Overview

Trail Name: Periodic Spring Trail
Location: Near Afton, Wyoming
Distance: 1.5 miles round trip
Elevation Gain: ~300 ft
Difficulty: Moderate (short but steady climb)
Average Time: 45–60 minutes
Best Season: June–October
Trailhead Coordinates: 42.749746, -110.860724
(42°44’58″N 110°51’34″W)

Access is via Swift Creek Lane / Forest Service Road 10211.

The final 3–4 miles of the drive are on a dirt/gravel road, but well-maintained. You do not need 4×4, although I always recommend it in Wyoming, just in case. The access road closes for winter on December 1st and reopens May 1st.

When to Visit for the Most Dramatic Experience

For the most dramatic experience, plan to visit this trail in September or October.

During peak spring runoff and early summer snowmelt, the water flow can be so heavy that it’s difficult to even tell the spring is intermittent. It often appears continuous because the mountain is saturated and water is pouring through the system nonstop.

In shoulder season, once runoff tapers off, the start-and-stop pattern becomes far more obvious.

You’ll clearly witness:

  • The full shutoff
  • The quiet pause
  • The low rumble building
  • The sudden surge of water rushing from the cliff

That contrast is what makes this place unforgettable. If you want the full “wait for it… wait for it…” experience, aim for early fall.

What Makes the Periodic Spring So Unique?

Periodic Spring (also called Intermittent Spring) doesn’t flow continuously. Instead, it pulses.

Water surges from the mountainside for several minutes, then the flow begins to slow. Finally it stops completely and silence returns. Then the rumbling begins again.

This cycle typically repeats every 10–20 minutes, depending on water levels.

The Science (At least the way I understand it!)

While not fully understood, scientists believe the spring operates like a natural underground siphon system. Picture a hidden chamber filling with water. Once it reaches a tipping point, gravity triggers a siphon effect, rapidly draining the chamber until it empties. Then it refills. And the cycle repeats.

It’s geology doing something that feels almost mechanical. I can’t help but stand there visualizing hidden tunnels and underground reservoirs filling and draining beneath my feet.

Is It Family Friendly?

Absolutely.

We’ve taken our adult daughters up, and they loved it. The start-and-stop feature is what makes it so memorable. Kids (and adults) are fascinated by the unpredictability.

A few notes for families, especially with young children:

  • Stay back from slick rock areas.
  • Supervise children near the water surge.
  • Dogs are allowed and may be off-leash in some areas.
  • Expect to encounter other hikers, it’s popular for a reason.

It’s short enough for most kids, but interesting enough to hold their attention.

What to Expect on the Hike

  • Gradual incline through forest
  • Occasional rocky sections
  • Well-defined trail
  • Beautiful canyon scenery
  • The unmistakable roar once the water returns

Even if you’ve hiked waterfalls before, this feels different. It’s not constant beauty, it’s anticipation.

Tips for Visiting Periodic Spring

  • Plan to stay at least 30–40 minutes to witness multiple cycles.
  • Check recent conditions if visiting in late fall.
  • Bring layers, mountain temps shift quickly.
  • Combine this with other Swift Creek Canyon stops for a half-day adventure.
  • Don’t rush. The waiting is part of the experience.

Why It’s Worth the Trip

There’s something deeply satisfying about watching nature surprise you. You stand there in silence, wondering if maybe that was the last surge. And then the rumble builds again.

It reminds you that not everything is constant. Some things operate on hidden rhythms. And sometimes the best experiences are the ones that start with stillness, and end with a roar.