For erosion insight and trail grades see this page
USDA Web Soil Survey- find your soil type on an interactive USDA soil map
4 DIY soil survey methods
How do you know what’s in your trail site soil horizon? By taking samples and testing them:
METHOD 1: the Ribbon Test
Roll a handful of moist soil into a tube shape with both hands. Squeeze it between your thumb and forefinger to form the longest and thinnest ribbon possible.
|Sand||Grainy||Can’t form a ribbon|
|Loam||Soft with some graininess||Thick and very short|
|Silt||Floury||Makes flakes rather than a ribbon|
|Sandy Clay||Substantial graininess||Thin, fairly long—50 to 76 mm (2 to 3 inches)—holds its own weight|
|Clay||Smooth||Very thin and very long—76 mm (3 inches)|
The tread surface should match the inte
METHOD 2: USDA guide to texture by feel (shown below the horizons)
First let me say that trail tread should be on the subsoil/mineral soil B and/or parent rock C, or bedrock R, a little A is OK. O should be removed during construction if it exists (in desert climates it may be very thin or non-existent). Enough use can start to displace O depending on its depth and user numbers. This approach however, can create a trough, and a berm that won’t allow water to escape the trail. It’s best to remove O and the outside berm as well to establish outslope that will allow water to sheet flow off the trail, not down it.
METHOD 3: Mason Jar Method (link to protocol)
- LABORATORY CLASSIFICATION OF SOILS FOR ENGINEERING PURPOSES