Technical Abstract: Thousands of bee species nest in the ground, sometimes gregariously, digging tunnels whose excavated soil is pushed to the surface as tumuli. To quantify tumulus production across a landscape, nesting female alkali bees (Nomia melanderi) were censused for the 155 km2 Touchet Valley of seWA, where its nest sites are managed to pollinate alfalfa seed fields. Nine million nesting females collectively brought 96 tons of soil to the surface in their tumuli, much of which is subsequently eroded away by wind or rain. Even at this rate, however, the oldest populated nest site would have cumulatively lost only four cm to surface subsidence as a result of the past half century¿s nesting activity.