A particular concern was the possibility of flooding in areas downstream from the burned zone. The town of Los Alamos, the national laboratory, and the lower parts of the burned area are all situated on the Pajarito Plateau, an area of extensive canyons and mesas in which surface runoff tends to concentrate in the canyon bottoms. This tendency was exacerbated in Cerro Grande's aftermath because the soil in the burned areas had become hydrophobic, raising the specter of drastically increased water flow in the streams in the canyons that the existing streambeds might not have been able to handle. This concern, coupled with the prospect of monsoon rains that typically begin in about July in the area, made dealing with the possibility of flooding urgent.