Mostly dark, mesa-forming basalt deposited as lava flows. Rocks of this unit are widely exposed south of Camp Verde (Hickey Formation basalts), in the Mohon Mountains north of Bagdad, "The Mesa" east of Parker, and at other scattered locations in western Arizona. Rocks of this unit were not tilted by middle-Tertiary normal faulting except in a narrow belt from north of Phoenix to the northwest corner of the state. (8-16 Ma)
Moderately to strongly consolidated conglomerate and sandstone deposited in basins during and after late Tertiary faulting. Includes lesser amounts of mudstone, siltstone, limestone, and gypsum. These deposits are generally light gray or tan. They commonly form high rounded hills and ridges in modern basins, and locally form prominent bluffs. Deposits of this unit are widely exposed in the dissected basins of southeastern and central Arizona. (2-16 Ma)
Wide variety of granitic rocks, including granite, granodiorite, tonalite, quartz diorite, diorite, and gabbro. These rocks commonly are characterized by steep, northeast-striking foliation. (1600-1800 Ma)
Brown to dark gray sandstone grades upward into green and gray shale, overlain by light to medium gray or tan limestone and dolostone. This unit includes the Tapeats Sandstone, Bright Angel Shale, Muav Limestone, Temple Butte Formation and Redwall Limestone in northern Arizona, and the Bolsa Quartzite, Abrigo Formation, Martin Formation, and Escabrosa Limestone in southern Arizona. These rocks record intermittent sea-level rise and inundation in early Paleozoic time. (330-540 Ma)
Mostly dark, inconspicuously flat, low-lying or mesa-forming basalt deposited as lava flows. Rocks included in this unit are located almost entirely in the large volcanic fields south and west of Flagstaff, in smaller fields in northwesternmost Arizona, and in the Hopi Buttes volcanic field on the Navajo and Hopi Indian Reservations north of Holbrook. Original volcanic landforms have been obscured by erosion. (4-8 Ma)
Unconsolidated to strongly consolidated alluvial and eolian deposits. This unit includes: coarse, poorly sorted alluvial fan and terrace deposits on middle and upper piedmonts and along large drainages; sand, silt and clay on alluvial plains and playas; and wind-blown sand deposits. (0-2 Ma)
Lava, tuff, fine-grained intrusive rock, and diverse pyroclastic rocks. These compositionally variable volcanic rocks include basalt, andesite, dacite, and rhyolite. Thick felsic volcanic sequences form prominent cliffs and range fronts in the Black (Mohave County), Superstition, Kofa, Eagletail, Galiuro, and Chiricahua Mountains. This unit includes regionally extensive ash-flow tuffs, such as the Peach Springs tuff of northwestern Arizona and the Apache Leap tuff east of Phoenix. Most volcanic rocks are 20-30 Ma in southeastern Arizona and 15 to 25 Ma in central and western Arizona, but this unit includes some late Eocene rocks near the New Mexico border in east-central Arizona. (11-38 Ma)
Coarse relict alluvial fan deposits that form rounded ridges or flat, isolated surfaces that are moderately to deeply incised by streams. These deposits are generally topographically high and have undergone substantial erosion. Deposits are moderately to strongly consolidated, and commonly contain coarser grained sediment than younger deposits in the same area. (0.75-3 Ma)
Weakly to strongly metamorphosed volcanic rocks. Protoliths include basalt, andesite, dacite, and rhyolite deposited as lava or tuff, related sedimentary rock, and shallow intrusive rock. These rocks, widely exposed in several belts in central Arizona, include metavolcanic rocks in the Yavapai and Tonto Basin supergroups. (1650 to 1800 Ma)
Mostly porphyritic biotite granite with large microcline phenocrysts, with local fine-grained border phases and aplite. Associated pegmatite and quartz veins are rare. This unit forms large plutons, including the Oracle Granite, Ruin Granite, granite in the Pinnacle Peak - Carefree area northeast of Phoenix, and several bodies west of Prescott. (1400-1450 Ma)
Interbedded sandstone, shale, and limestone usually characterized by ledgy outcrops. Orange to reddish sandstone forms cliffs near Sedona. This unit includes Supai Group and Hermit Shale in northern Arizona and Naco Group in southern Arizona. It was deposited in coastal-plain to shallow-marine settings during time of variable and changing sea level. Rocks of this map unit in southern Arizona may be in part equivalent to Permian rocks of map unit P in central and northern Arizona. (280-310 Ma)
Con-glomerate, sandstone, mudstone, limestone, and rock-avalanche breccia (sheet-like deposits of crushed rock) deposited and tilted during widespread normal faulting and basin development. Sediments, mostly conglomerate and sandstone, are commonly medium to dark brown, reddish brown, or brownish gray; younger strata are generally lighter colors. Most deposits are 20 to 30 Ma in southeastern Arizona and 15 to 25 Ma in central and western Arizona. (11-32 Ma)
Metasedimentary rocks, mostly derived from sandstone and shale, with minor conglomerate and carbonate rock. Includes quartz-rich, mostly nonvolcanic Pinal Schist in southeastern Arizona and variably volcanic-lithic sedimentary rocks in the Yavapai and Tonto Basin supergroups in central Arizona. (1600-1800 Ma)
Unconsolidated deposits associated with modern fluvial systems. This unit consists primarily of fine-grained, well-sorted sediment on alluvial plains, but also includes gravelly channel, terrace, and alluvial fan deposits on middle and upper piedmonts. (0-10 ka)
Undivided metasedimentary, metavolcanic, and gneissic rocks. (1600-1800 Ma)
Gray to tan, cherty limestone of Kaibab and Toroweap Formations, and underlying white to tan, fine-grained Coconino Sandstone. Limestone was deposited in a shallow sea, and sandstone was deposited in near-shore dunes and beach settings. (270-280 Ma)
Unconsolidated to weakly consolidated alluvial fan, terrace, and basin-floor deposits with moderate to strong soil development. Fan and terrace deposits are primarily poorly sorted, moderately bedded gravel and sand, and basin-floor deposits are primarily sand, silt, and clay. (10-750 ka)
Unconsolidated to weakly consolidated sand and gravel in river channels and sand, silt, and clay on floodplains. Also includes young terrace deposits fringing floodplains. (0-10 ka)
Porphyritic to equigranular granite to diorite emplaced during the Laramide orogeny. Larger plutons are characteristically medium-grained, biotite +/- hornblende granodiorite to granite. Smaller, shallow-level intrusions are typically porphyritic. Most of the large copper deposits in Arizona are associated with porphyritic granitic rocks of this unit, and are thus named 'porphyry copper deposits'. (50-82 Ma)
Brown to maroon, resistant quartzite and minor conglomerate of the Mazatzal Group, exposed primarily in the Payson area. (1650? -1700 Ma)
Rhyolite to andesite deposited as lava flows and related rocks associated with basaltic rocks of map units Tby and Tb. (2-12 Ma)
Light colored, weakly to moderately consolidated conglomerate and sandstone deposited largely or entirely before mid-Tertiary volcanism and extensional faulting. Most sediment was deposited by early Cenozoic streams that flowed northeastward onto the Colorado Plateau from areas to the southwest that are now lower in elevation than the Plateau. Sediments of this map unit, other than the Chuska Sandstone in northeasternmost Arizona, are commonly referred to as "rim gravels" because they now rest on or near the Mogollon Rim, which is the southwestern edge of the Colorado Plateau. (30-65 Ma)
Sequences of diverse volcanic rocks with abundant interbedded sedimentary rocks. (11-32 Ma)
Gneissic rocks with complex histories, typically with well developed, light-colored granitoid layers and dark-colored biotite- and amphibole-rich layers. Protoliths are of Tertiary to Proterozoic age. This unit includes variably mylonitic gneisses in metamorphic core complexes that have been exhumed from middle crustal levels by large-displacement middle Tertiary normal faults, and gneiss exposed at scattered locations near the Colorado River in southwestern Arizona. These rocks are interpreted to record Proterozoic, Mesozoic, and Tertiary metamorphism and deformation. (15-1800 Ma)
Light-colored peraluminous muscovite granite with or without garnet; commonly forms sills and is associated with abundant pegmatite dikes and sills. This unit includes granites in the Harcuvar and Harquahala Mountains of western Arizona and in the Santa Catalina, Rincon, Tortolita, Picacho, and Coyote Mountains of south-central Arizona. These granites typically represent the youngest phase of voluminous magmatism during the Laramide orogeny in Arizona. This unit also includes several muscovite-bearing granites in southern Arizona that are associated with calc-alkaline granites of unit TKg, and a batholith in the Cabeza Prieta area of southwestern Arizona. (50-80 Ma)
Rhyolite to andesite and closely associated sedimentary and near-surface intrusive rocks; commonly dark gray to dark greenish gray or greenish brown. In the ranges west of Tucson, this unit includes thick welded ash-flow tuffs. Volcanic rocks of this unit are inferred to be derived from vents and volcanoes above magma chambers that solidified to form the granitic rocks of map unit TKg. These rocks are restricted to southeastern Arizona except for a small outcrop near Bagdad. (50-82 Ma)
Undivided Early and Middle Proterozoic granitic rocks (units Xg and Yg). (1400-1800 Ma)