Geology Legend

San Pedro Geology Legend

Qy	Young Alluvium	Holocene - late Pleistocene	Sand and gravel in stream channels; sand, silt, and clay on flood plains and playas.
Q	Surficial Deposits	Holocene – middle Pleistocene	Sand and gravel in present-day valleys, and wind-blown sand
Qo	Older Surficial Deposits	Middle Pleistocene – latest Pliocene [?]	Sand, gravel, and sparse wind-blown sand; undergoing erosion
Tsy	Sedimentary Rocks	Pliocene – middle Miocene	Conglomerate and sandstone deposited in basins during and after late Tertiary faulting; includes light gray mudstone, sandstone, limestone, and gypsum; forms some prominent bluffs in modern valleys
Tvy	Volcanic Rocks	Pliocene – middle Miocene	Rhyolitic to andesitic lava flows and related rocks
Tsm	Sedimentary Rocks	Middle Miocene – Oligocene	Conglomerate, sandstone, mudstone, and landslides deposited and tilted during a period of faulting; red-brown; younger parts are buff to gray.
Tv	Volcanic and Sedimentary Rocks	Middle Miocene – Oligocene	Lava flows and tuffs with less abundant sedimentary rocks; thick welded tuffs form prominent physiographic features
Tg	Granitic Rocks	Early Miocene – Oligocene	Granite and granodiorite
TKgm	Granitic Rocks	Early Tertiary - Late Cretaceous	Light-colored granite; commonly contains muscovite and garnet; associated with abundant pegmatite dikes
TKg	Granitic Rocks	Early Tertiary – Late Cretaceous	Granite to diorite and near-surface porphyry; associated with copper deposits
Kv	Volcanic Rocks	Early Tertiary – Late Cretaceous	Rhyolite to andesite with associated sedimentary and near-surface intrusive rocks; commonly dark gray to green and highly fractured
KJs	Sedimentary Rocks with Minor Volcanic Rocks	Cretaceous – Late Jurassic	Sandstone and conglomerate, rarely forms prominent outcrops; conglomerate typical near base of unit, and locally in upper part; nonmarine except in southeastern Arizona, where prominent gray marine limestone forms middle of the Bisbee group
Jg	Granitic Rocks	Jurassic	Granite to diorite, locally sheared
Jsv	Sedimentary and Volcanic Rocks	Jurassic	Massive quartz-feldspar porphyry, probably welded tuff; associated with sandstone and conglomerate derived from volcanic rocks; reddish brown sandstone and mudstone at base in southeastern Arizona
Jv	Volcanic Rocks	Jurassic
PP	Sedimentary Rocks	Permian – Pennsylvanian	Interbedded sandstone, shale, and limestone usually characterized by ledgy outcrops; orange to reddish, cliff-forming sandstone near Sedona; includes Supai Group and Hermit Shale in north and Naco Group in south; deposited in coastal-plain to shallow-marine settings during cyclic rise and fall of sea level
MC	Sedimentary Rocks	Mississippian, Devonian, and Cambrian	Brown to dark gray sandstone grades upward into green and gray shale, overlain by light to medium gray limestone and dolomite. Records intermittent sea-level rise and inundation of continent in early Paleozoic time
Ys	Sedimentary Rocks	Middle Paleozoic	Red-brown shale and sandstone, buff quartzite, limestone, basalt, black shale, and sparse conglomerate; Grand Canyon Supergroup and Apache Group; deposited in shallow marine, coastal marine, and river settings
Yg	Granitic Rocks	Middle or Early Proterozoic	Wide variety of granitic rocks; biotite granite with large feldspar crystals common
Xg	Quartzite	Early Proterozoic	Brown to maroon quartzite and conglomerate of Mazatzal Group, mostly resistant to weathering
Xm	Metamorphic Rocks	Early Proterozoic	Sedimentary and volcanic rocks metamorphosed to schist and gneiss; Yavapai Supergroup and Pinal Schist