In the valleys, erosional features and steep slopes with colluvial deposits (material deposited by gravity) are very common. The terraces are primarily silt loam and sandy loam deposits which accumulated on the bed of the glacial Fraser River. The current Fraser River and Churn Creek have downcut into the glacial deposits and, as a result, the valley bottoms are relatively narrow and little floodplain is present.

The plateau is underlain by thick basaltic rock from ancient lava flows overlain by basal moraine deposited beneath glaciers. Many areas have a veneer of wind deposited aeolian material overlying the basal moraine.

The Lower Grasslands are the hottest, driest grasslands; they occupy lower and middle slopes (up to 650m) of the Fraser River valley. The Lower Grasslands are closely related to other low elevation grasslands in main valley systems of southern B.C. and to the sagebrush-bunchgrass grasslands of the northwestern U.S.

Climax vegetation is dominated by bluebunch wheatgrass, scattered to abundant big sagebrush, and a soil crust of lichens and dryland mosses (microbiotic crust). Other commonly occurring plants include needle-and-thread grass, sand dropseed, Sandberg's bluegrass, junegrass, prickly pear cactus, and pasture sage. Vascular plants often cover less than 50% of the soil surface while the microbiotic crust may cover up to 80% of the soil surface. Bluebunch wheatgrass typically decreases while the other grasses initially increase with grazing. Big sagebrush has probably increased with grazing and fire suppression.

Productivity is much lower and vegetation recovery following disturbance is much slower than in the Middle and Upper grasslands.

Soils of the Lower Grasslands are predominantly Brown Chernozems. Organic matter levels in the Ah are lower than in the middle and upper grasslands and the Bm horizon is often more calcareous. Soils are developed primarily in silt loam to sandy loam fluvial deposits that are often gravelly.

The Middle Grasslands occur on the middle and upper slopes of the Fraser River valley and lower reaches of the Churn Creek valley. They occupy a band between the Lower and Upper grasslands at elevations of about 650 m and 800 m. They are cooler and moister than the Lower Grasslands but warmer and drier than the Upper Grasslands. The topography includes gullied valley slopes, colluvial slopes, fluvial terraces, basal moraine, bedrock cliffs and escarpments, and cliffs of unconsolidated fluvial deposits.

Late seral and climax vegetation is dominated by bluebunch wheatgrass, needle-and-thread grass, junegrass, and a microbiotic crust. Total plant cover of species is typically greater than in the Lower Grasslands. Productivity and the diversity of vascular plant species is higher than in the Lower Grasslands but lower than in the Upper Grasslands.

With persistent heavy grazing of bluebunch wheatgrass, its abundance declines and other grasses including needle-and-thread grass, junegrass, and sand dropseed tend to initially increase in cover. With continued heavy grazing, these species also decrease in cover and are largely be replaced with more weedy native forbs such as pussytoes, fleabanes and pasture sage.

Soils are predominantly Orthic Brown or Dark Brown Chernozems with a 15 - 30 cm thick organic-rich surface (Ah) horizon which occurs primarily in the silty aeolian cap that covers most morainal deposits of the area.

Upper Grasslands occur above the Middle Grasslands on upper slopes of the Fraser River Valley and on the adjacent plateau. They also occur on the plateau adjacent to the Churn Creek Valley as far west as the western edge of the protected area. Elevations are 800 -1200 m on a predominantly level to gently rolling landscape. The vegetation is a mosaic of grasslands, Douglas-fir forests, and aspen forests.

The upper grasslands are in a transition from open grassland to forest. Vegetation shifts from forest to grassland and from grasslands to forest in response to small local changes in climate, site or historical factors. The resulting landscape is a mosaic of forest and grassland in which the forest occurs predominantly on cooler, moister sites and the grasslands on warmer, drier sites. Soil differences may also contribute to the current pattern of forest and grassland.

Relatively undisturbed grasslands are dominated by bluebunch wheatgrass, short-awned porcupine grass and spreading needlegrass. Small patches dominated by one of the latter two grasses often occur within a matrix of all three species. In contrast to the Upper Grasslands of the Thompson and Okanagan to the south, neither rough fescue nor Idaho fescue occurs in these Upper Grasslands. Plant cover is nearly continuous and a thick litter layer is often present where fires have not occurred recently. A very diverse forb, graminoid, and lichen flora is present.

Soils in the Upper Grasslands are most often developed in a veneer (20 - 50 cm thick) of silty or loamy aeolian materials over basal moraine. Soils are predominantly Dark Brown Chernozems with a 15 - 30 cm thick organic-rich surface mineral (Ah) horizon. The Ah horizon is generally darker (contains more organic matter) than in the Middle Grasslands.