The Front Range, Longmont to Monument.

Bentonite clay and claystone of the Denver Basin, the most common ground in the metro. Bentonite swells when it gets wet and shrinks when it dries, so the ground under a slab is never quite the same height two seasons in a row.

Remove the soft and organic soil, bring in compacted road base, set rebar on chairs, and plan joints and slope so water runs away from the house instead of soaking the clay beside it.

Steep lots along the hogback, where claystone and shale layers tilt up toward the mountains. Along the foothills the bedrock layers stand nearly on end.

Deeper excavation and a thicker compacted base, reinforcement sized for uneven support, and drainage that intercepts runoff above the slab, often paired with a retaining wall where the grade demands it.

Sand, gravel and silt laid down along the South Platte, Clear Creek and St. Vrain. River soil drains far better than clay and does not swell.

Compaction done in lifts, geotextile fabric where the native soil is soft, and a thicker section anywhere a truck, trailer or RV will park.

The high ridge between Denver and Colorado Springs, roughly 6,000 to 7,300 feet, on sandy soils with clay seams. Elevation is the story here.

Air-entrained exterior mix, proper curing, a penetrating sealer before the first winter, and a broom texture for traction on sloped driveways.