Incahuasi Central Volcanic Zone of the Andes together with about 110 other Quaternary volcanoes, and lies in the southern sector of the volcanic zone; other volcanic zones in the Andes are the Northern Volcanic Zone, the Southern Volcanic Zone and the Austral Volcanic Zone. The history of volcanic activity is poorly known for most of these volcanoes owing to the lack of dating; only a few historical eruptions have been recorded, such as an eruption at Ojos del Salado in 1993. Incahuasi is located northeast of Ojos del Salado, the highest volcano in the world. Both volcanoes are found at the
Siskiyou Mountains 1910, pears had begun to replace apples as the major fruit grown in the region. In 1927, the Jackson County seat moved to Medford, which had become much larger than Jacksonville. The highest peaks in the range include Mount Ashland at an elevation of , Dutchman Peak at , Siskiyou Peak at , and Wagner Butte at , all of which are in Oregon. The highest peak in the California portion of the range is Preston Peak at . There are also several lower mountains, including Negro Ben Mountain, which reaches . The main drainage basins in the mountains are