Protecting Rare Frogs in Fairfax

by Sandy Guldman

Marin County has two populations of the foothill yellow-legged frog, a species listed as endangered by the state. One is found in Little Carson and Big Carson creeks on Marin Water land; the second, in San Anselmo and Cascade creeks in the Cascade Open Space Preserve (OSP) managed by Marin County Parks.

One of the biggest threats to these frogs is instream habitat disturbance. The Marin Water habitat is more remote and less likely to be disturbed, although a roster of volunteer docents protects the frogs at Little Carson Falls.

In contrast, the Cascade OSP is a popular recreational area and the main trail through the OSP crosses the creek four times! Each crossing poses a threat to the frog population, as egg masses and frogs are easily crushed.

The Cascade Trail Bridges project would replace these four fords with two 6-foot-wide trail bridges, protecting the aquatic habitat required for frog breeding, tadpole development, and adult survival. Why aren’t all local environmentalists actively supporting this project, which provides major environmental benefits? What are the arguments against the trail bridges?

The first argument is that the trail bridges would lead to increased visitation to the OSP, damaging in and of itself. However, no evidence has been provided to support the assertion that more people would use it. Large numbers of people visit the OSP, attracted by the creek, the waterfall, and the inkwells. Use of all open spaces and parks has increased during the pandemic, making it even more important to keep users out of sensitive habitat. Access for hikers is greatly restricted by the limited available parking on Cascade Drive.

When the creek is flowing, hikers currently use the High Water Trail. If the bridges are built, the High Water Trail would be decommissioned. The trail bridges would not provide more access, just replace an erosive, unstable trail or wet creek crossings with environmentally friendly trail bridges. Bridge opponents also think that more mountain bikers would use the OSP. Although the mountain biking community is in favor of the bridges, it does not see the project as improving access connection; bikers already use the fords when traveling to or from Pine Mountain. Biking through a wet crossing is not a major deterrent, but many cyclists commented that they would like to see better protection for sensitive aquatic habitat and would rather use trail bridges instead of riding through the creek.

Second, opponents cite potential impacts to dusky-footed wood rats and northern spotted owls. Surveys conducted by Parks’ biologists found abundant wood rat nests, but none that would be disturbed by the proposed trail bridges. Similarly, northern spotted owl nests are located a safe distance from construction areas. Furthermore, immediately before construction could begin, additional surveys would be conducted to document that new nests near construction areas have not been built.

Please support protecting the Corte Madera Creek watershed’s only yellow-legged frog population, along with other important aquatic resources like steelhead/rainbow trout also found in the Cascade Canyon OSP, and let the Fairfax Town Council and Marin County Board of Supervisors hear your voice.