Oregon is divided into 17 Major Land Resource Areas, the largest of which include the Malheur High Plateau, the Cascade Mountains, the Blue Mountain Foothills, and Blue Mountains. The single most important geologic event in Oregon was the deposition of Mazama ash 7,700 years by the explosion of Mt. Mazama. Oregon has soil series representative of 10 orders, 40 suborders, 114 great groups, 389 subgroups, over 1,000 families, and over 1,700 soil series. Mollisols are the dominant order in Oregon, followed by Aridisols, Inceptisols, Andisols, Ultisols, and Alfisols. Soils in Oregon are used primarily for forest products, livestock grazing, agricultural crops, and wildlife management. Key land use issues in Oregon are climate change; wetland loss; flooding; landslides; volcanoes, earthquakes, and tsunamis; coastal erosion; and wildfires.