This Section of the PCT Has Been Closed for 20 Years. The Reason? MYLFs

If you’ve hiked the Pacific Crest Trail, chances are you’re familiar with the Williamson Rock closure — nicknamed the “frog closure” — in Southern California. This closure covers a 3.6-mile section of the PCT and was implemented 20 years ago for the protection of the Southern California mountain yellow-legged frog and its critical habitat.

An Overview of the PCT Frog Closure: Where and Why?

Photo: James Townsend

The Williamson Rock closure, within the Angeles National Forest of Southern California, has been in place for more than two decades, beginning in 2005. It specifically restricts access to the PCT between FarOut northbound mile markers 390.2 (Hwy 2, Eagles Roost Picnic Area) and 393.8 (PCT/Burkhart Trail intersection).

The closure is marked with a sign at the mile 390.2 road crossing that reads, “Notice: in an effort to allow the U.S. Forest Service to follow guidelines for protecting the habitat of the mountain yellow-legged frog, an endangered species, this area is closed until further notice.” Violating the closure could result in a fine of up to $5,000, six months in jail, or both (see Forest Order No. 05-01-24-04).

While the PCTA currently offers no official detour, hikers have long respected the closure by finding alternate routes around this sensitive habitat. Some of the commonly used reroutes are outlined later in this article. 

In August 2024, the US Fish and Wildlife Service released its 5-Year Review of the species, offering new insights into the status and recovery of the mountain yellow-legged frog along the Southern California PCT corridor. This article aims to explain the findings of that review and explore what they might mean for the future of this long-standing trail closure.

“Yellow-legged frog on a rock” by USFWS Pacific Southwest Region is licensed under CC BY 2.0.

The Southern California Mountain Yellow-Legged Frog (MYLF)

The Southern California mountain yellow-legged frog (Rana muscosa) is often abbreviated as MYLF (no, not MILF, MYLF). It is a frog species endemic to California, meaning it is only found here, nowhere else in the world. In 2002, the MYLF was officially declared an endangered species under the Endangered Species Act.

MYLFs throughout California were long considered to be one single species until 2007. However, thanks to genetic testing, we now know there are actually two distinct species of MYLFs in the state.

The species relevant to this article is the Southern California MYLF, occupying the southern range of the Sierra and the Transverse Ranges of Southern California. The second species is the Sierra Nevada MYLF, which exists in the northern Sierra, above the Tehachapi Mountains. Both are federally listed endangered species.

The Southern California MYLF lives in mountain lakes, ponds, and streams, and breeds by depositing free-floating eggs in shallow waters or underwater attached to rocks. After these eggs hatch, the tadpoles need a permanent water source for at least two years while they develop, which can be a challenge during years of drought or fire in southern California. 

How to Identify a MYLF

The adult MYLF is yellow, brown, or olive colored with variable black and brown markings and has characteristically yellow-hued legs and underbellies. Adults range from 4 to 8.9 centimeters long, with females usually being larger than males. When handled, MYLFs release a garlic-smelling odor in defense. Note: It is illegal to handle any federally listed species without the proper permit(s).

“Mountain yellow-legged frog” by USFWS/Rick Kuyper is licensed under CC BY 2.0.

The 5-Year Review: What has happened to Southern California MYLF populations in the last five years?

In August 2024, the USFWS released its 5-Year Review of the Southern California MYLF. A review is required for each species listed under the Endangered Species Act with the purpose of providing an update on species wellbeing and recovery efforts. For the MYLF, a lot has happened since the last review in 2019.

Species recovery efforts have expanded, and translocations (moving individuals from one area to another) have been done with both wild-caught and captive-bred individuals in hopes of boosting frog numbers in the wild. Collected data indicated these efforts have started to pay off.

The 2019 review cited 10 known populations of Southern California MYLF, while the 2024 review cited 19 known populations. This is a move in the right direction, but there’s still a long way to go. Records show there were once at least 166 known populations across southern California. Existing populations are living in a highly fragmented environment.

According to the review, the top threats currently faced by the MYLF population of Little Rock Creek (within the PCT closure) are recreation, wildfire, and road maintenance, in that order. Adult MYLF numbers at this site rose from 32 in 2020 to 140 in 2023, nearing the area’s record high.

But things took a devastating turn in 2024, when surveys found just one adult individual. This area, closed to PCT hikers and other trail users, has long been a stronghold for the species. Last year’s sharp in frogs here is both drastic and alarming for biologists.

How Habitat Change Hurts MYLFs

The review cites the introduction of nonnative trout as a primary reason for the decline in frog populations, with trout acting as a major predator of the MYLF. Trout eradication has been a central focus of MYLF conservation efforts — successful in some areas, but less so in others due to “inadequate fish barriers.”

While aquatic predators pose one threat for MYLFs, environmental disturbances such as wildfire present another. These increasingly frequent events can dramatically alter or destroy critical frog habitat, especially in high-elevation watersheds where the species exists today. Wildfires not only reduce available habitat but can also introduce sediment, alter hydrology, and compromise stream quality long after the flames are extinguished.

After the Bobcat Fire burned over 115,000 acres of the San Gabriel Mountains in 2020, MYLF tadpoles were rescued from various burn zones and transported to captive breeding programs. Many of these individuals were later reintroduced into the wild in 2023.

Even with varying levels of success across Southern California, all remaining MYLF populations remain very fragile at the time of this review. Future conservation efforts include continuing eradication of nonnative trout, management of human impact, wildfire monitoring, and additional suitable habitat identification for future translocations.

Figure 1. Survey results of captured unique adult southern California MYLF over the 19-year period of PCT closure at Little Rock Creek

So, what does all of this mean for the PCT frog closure near Little Rock Creek?

Back in 2019, Outside Magazine reported that the US Forest Service was considering a plan to construct a bridge over the creek within the closure zone. The idea was to allow PCT hikers to cross the sensitive MYLF habitat with minimal disturbance. A Draft Environmental Impact Statement (DEIS) had been released, and public comments were accepted through September 2018. A Final Environmental Impact Statement (FEIS) was originally expected by August 2022.

However, as of April 2025, the FEIS has not yet been finalized, and no decision has been made regarding the bridge proposal. This delay is likely due to continued coordination between the US Forest Service and the US Fish and Wildlife Service to ensure any action taken complies with the Endangered Species Act.

Meanwhile, the MYLF remains federally listed as endangered, with the US Fish and Wildlife Service recommending that this status remain in place for the foreseeable future. Due to the sharp population decline in 2024, the area within the current trail closure will likely be monitored closely, and conservation efforts will continue.

These efforts, including captive breeding and the translocation of both wild-caught and captive-raised individuals, will continue throughout the frog’s native range. Until a decision is made about the proposed bridge project, the Williamson Rock closure remains in effect. For now, hikers are expected to continue rerouting around the area to protect this fragile amphibian population and the habitat that sustains it.

Walking Highway 2 to reroute around the Williamson Rock closure. Image credit: Kelsey Nannini, 2022

Help Protect the Southern California MYLF

We remain hopeful that MYLF populations will continue to recover, and that a bridge over Little Rock Creek may allow this 3.6-mile section of trail to reopen to PCT hikers. In the meantime, it’s essential to keep the well-being of this endangered species a top priority.

These frogs rely on intact, undisturbed habitat to survive, and as stewards of the environment, we play a critical role in their recovery. Respecting trail closures isn’t just about following rules — it’s about helping ensure the long-term success of a species that has nearly disappeared from Southern California’s backcountry.

3 Common PCT Frog Closure Reroute Options for Thru-Hikers

Photo: James Townsend

(Note: these are not official reroutes provided by the PCTA. Please do your own research on each route and, as always, travel at your own risk.)

1. Highway 2 road walk until Buckhorn Junction (~4.8 miles): Sometimes called the Buckhorn Camp detour, this reroute follows Highway 2 for 2.8 miles until heading up the Burkhart Trail another 2 miles to meet back up with the PCT at mile 394.0. This is likely not officially recommended by the PCTA because it is along a main highway. However, Highway 2 is closed during the winter and early spring to vehicular traffic. You can check to see if this road is currently open to vehicles here.

2. Highway 2 road walk (~5 miles): This road walk follows Highway 2 until it intersects with the PCT at mile 398.0.

3. Williamson-Pallet-Burkhart Saddle (~10.5 miles): A reroute that keeps you on a trail instead of a road, taking you up and around the protected frog habitat via Pleasant View Ridge (past Williamson Peak, past Pallett Mountain) to Burkhart Saddle and down Burkhart Trail, meeting back up with the PCT near Cooper Canyon Falls.

Respect trail closures and the wildlife they protect by taking alternate routes whenever possible — your cooperation helps keep these habitats safe. Godspeed, frogs! To safer ponds ahead!