As one proceeds south within the Sonoran Desert the winter season is less severe, where more subtropical and tropical elements appear. Winter frosts are common, but not severe. Succulent cacti, highly drought tolerant shrubs, and thorny shrubs are equally common. Towards the north, especially on mountain slopes, the vegetation merges towards chaparral type vegetation which is characterized by dense thickets of evergreen shrubs that are also fire adapted. Then towards the northwest the Sonoran merges with the Mohave Desert where summer rainfall is usually scarce.
Vegetation consists mostly of highly drought tolerant shrubs with few succulent cacti.
Drought deciduous trees and shrubs become increasingly common towards the south, many of which are quite thorny. Succulent cacti are abundant and diverse. The Sonoran Desert rather gradually merges into the more southerly Tropical Dry Thorn Forest of Southern Sonora and Sinaloa. Cool moist weather comes in winter, the summers are not quite as hot due to the cooling effect of the Pacific Ocean, and occasionally summer brings good amounts of rainfall. Succulents including cacti, agaves and yuccas are abundant and extraordinarily diverse.