The Science of Soil

The impact of mountain bikes
on Forest Park soil

Forest Park soil is categorized as Cascade Silt Loam. It is comprised of wind-blown silt loam that came off the Columbia River flood plains for the last 2.6 million years. It’s easily mobile.

Hiking and walking compact this type of soil with little or no erosion or pollution to the watersheds in Forest Park. The impact of mountain bikes on this delicate soil composition is a different story.

Every time it rains the soil erodes, gets muddy, then dries out and blows off. The effect of braking and accelerating on a mountain bike (creating coveted rooster tails) causes the soil to be ripped up. Ruts and shreds become polluted. Silt-filled puddles and streams run downhill into streams feeding into Forest Park watersheds with sediment and pollution. This can impact watershed quality for humans, wildlife and fish.