The Black Canyon City and Squaw Creek Mesa 7.5 minute quadrangles are located north of the Phoenix metropolitan area within the Transition Zone, an area of rugged topography, roughly 100 kilometers wide in central Arizona that separates the Basin and Range and Colorado Plateau physiographic provinces in Arizona (Figure 1). Low- to moderate-relief terrain occupies the center portion of the map area, with rugged, high-relief terrain of the New River Mountains to the east and the Bradshaw Mountains to the west. Elevations range from 1800 feet along the Agua Fria River at the southern edge of the map to just under 6000 feet in the mountainous areas to the east and west. The southern ends of Black Mesa (3000-3200 feet) and Perry Mesa (3400-3600 feet) are located along the northern border of the map area. Other prominent mesas include Williams Mesa and Squaw Creek Mesa.