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QUIZ: GEOLOGY OF THE SOUTHWEST
Sources: PowerPoint 04e, Web1, Web2, text (p. 71-85)
1. Sierras: Farallon Plate subducts under NA Plate producing
volcanic mountain chain.
Rockies: Farallon Plate subducts under NA Plate at low angle and "sticks", causing compression on the NA Plate which creates the Rockies by thrusting and folding.
Basin and Range: After the last of the Farallon Plate subducts beneath the NA Plate, crustal extension occurs, producing a series of normal faults throughout the southwest, causing down-dropped valleys (basins) and uptilted mountains (ranges).
Colorado Plateau: uplifted block; don't know why
2. Large volcano collapses and forms Caldera. Crustal extension causes Detachment Fault that moves Tucson Mt. Caldera 20 miles to the southwest (to approximately where Tucson Mountains are today). Further crustal extension (the Basin and Range Disturbance) produces a series of normal faults, dropping down Tucson Valley and lifting up Tucson and Catalina Mountains. Erosion has resulted in current form of Tucson Mts., Tucson Basin, and Santa Catalinas.