Pima County, including Tucson, is located in the Arizona Upland of the Sonoran Desert. The Arizona Upland has five seasons, opens a new window.
"Tucson is the only major city located in Arizona Upland."
"This northeastern section, mostly in south-central Arizona and northern Sonora, is the highest and coldest subdivision of the Sonoran Desert. The terrain contains numerous mountain ranges, and the valleys are narrower than in the Lower Colorado River Valley subdivision. Trees are common on rocky slopes as well as drainages, and saguaros are found everywhere but on the valley floors. This community is also called the saguaro-palo verde forest. It is the only subdivision that experiences frequent hard winter frosts, so many species of the lower elevation and more southerly subdivisions cannot survive here."
"An ever-increasing number of biologists is concluding that the Arizona Upland's climate, vegetation density, and biodiversity resemble thornscrub more than desert. Don't be surprised if this subdivision is reclassified as thornscrub in the future."
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