Seitz Soil Series

The Seitz soil series is Colorado's recognized state soil. It sits on the steep hill and mountain slopes of the southern Rocky Mountains — ground covered in Engelmann spruce, subalpine fir, and Rocky Mountain Douglas-fir, at elevations where the growing season lasts as few as 40 days.

Seitz soil is full of rocks. The technical classification calls it 'clayey-skeletal' — more than 35 percent of the soil volume is rock fragments, pieces broken from the surrounding peaks of granite, gneiss, schist, rhyolite, and basalt. Those fragments work their way downhill over centuries, mixing into the soil as colluvium. The result is a soil that is deep, well-drained, and too rocky and steep for any plow.

Soil scientists at the USDA Natural Resources Conservation Service selected the Seitz series to represent Colorado because it captures the landscape that defines the state: the forested, high-elevation mountain slopes of the southern Rockies. More than two-thirds of Colorado sits above 6,000 feet, and the Seitz series covers the mountain heart of that terrain.

The Seitz series was first established in 1972 in Rio Grande County, where the type location sits about 11 miles southwest of Monte Vista. It takes its name from the Seitz stream near the original description site.

Colorado's Legislature has not passed a formal law designating a state soil. The Seitz series is recognized by the USDA as Colorado's representative state soil, chosen by Colorado soil scientists to represent the mountain landscape that most defines the state's geography, economy, and identity.

Digging into Seitz soil means working around rocks — constantly. Below a thin mat of organic duff from fallen needles and decaying wood, the soil darkens for a few inches, then fades to a pale, washed-out gray before dropping into a brown clay zone packed with angular rock fragments. Every horizon is stony. The deeper you go, the more rocks there are.

Seitz soil covers about 350,000 acres across 17 counties in south-central and southwestern Colorado — the mountain terrain of the San Juan Mountains, the Rio Grande headwaters, and the ranges of the southern Rockies.

Slopes range from 2 to 65 percent, and elevations run from 7,500 to 12,000 feet. The soil forms on hill and mountain sideslopes where colluvium — rock and soil material that slowly slides and creeps downhill — gathers over centuries.

The series is found in Colorado and extends into northern New Mexico. Within Colorado, the core area is the southern Rocky Mountains, where ancient igneous and metamorphic peaks shed the rock fragments that become Seitz soil.

Seitz soil does not support farming. The slopes are too steep, the rocks too numerous, the growing season too short — only 40 to 80 frost-free days per year. Instead, this soil holds some of Colorado's most important forests: Engelmann spruce, subalpine fir, and Rocky Mountain Douglas-fir.

These forests sit at the headwaters of major river systems. The snowpack that accumulates on Seitz soil slopes through winter melts slowly into the Rio Grande, Arkansas, and other rivers that supply water to Colorado cities and seven downstream states. In this sense, Seitz soil is one of Colorado's most critical natural resources — not for what it grows, but for what it holds.

Most land on Seitz soil is managed for forestry, wildlife habitat, and outdoor recreation. Skiing, hiking, hunting, and fishing are the main economic uses. Some gentler Seitz slopes support native pastureland used for summer grazing by cattle and sheep.