The geology of the Uqlat as Suqur quadrangle provides a detailed record of the late Proterozoic layered and intrusive rock units,-their interrelationships, and the structural evolution of a large portion of the northeastern Shield of Saudi Arabia. Four major unconformities and three well-defined intrusive episodes identified in the quadrangle provide a rational basis for describing and defining lithostratigraphic units, and for interpreting the deformational history within the region. The oldest rocks consist chiefly of low-potassium mafic and felsic metavolcanic rocks (Dhiran meta-andesite) that were intruded 690 Ma to at least 680 Ma ago by the (possibly cogenetic) Suwaj suite, represented in this quadrangle by low-potassium microdiorite and granodiorite granophyre. The Dhiran-Suwaj terrane was deformed and metamorphosed during a regional erogenic event and became the principal source of clastic material for the Murdama group, which was deposited in subsiding marine basins marginal to emergent highlands. Coarse conglomerate and shallow-water limestone were characteristically deposited near these margins, whereas thick, monotonous sandstone accumulated in the deep-water basin centers. The unlithified Murdama deposits were .gently deformed but regionally folded along north-south trends between rigid blocks-of the Dhiran-Suwaj terrane after about 650 Ma. Regional extension and volcanic activity began at about 640 Ma and produced voluminous calc-alkaline andesite, volcaniclastic sandstone, and volcaniclastic conglomerate of the Jurdhawiyah group. Primary volcanic materials and their rapidly eroded detritus were deposited in linear (probably fault-bounded) basins that were partly shallow-water marine and partly terrestrial. The largest Jurdhawiyah basin began to warp and close during the waning stages of volcanic activity in response to northward-directed compression. High-angle reverse faults displaced the southern basin margin, and a fault-bounded structural arch rose along the northern margin and shed coarse debris into the basin. This intense deformation was closely followed by intrusion of voluminous calc-alkaline granodiorite, diorite, and granite (Idah suite), 620 Ma to 615 Ma ago, that may have been cogenetic with the Jurdhawiyah volcanic rocks. Mineralization is widely associated with this intrusive episode, in the form of gold-bearing quartz veins within and marginal to these plutons. Uplift, erosion, and probable planation characterized the subsequent interval of about 30 Ma, during which no rocks are known to have formed. Beginning at about 585 Ma during a period of regional cratonic extension, high-silica peraluminous granite magma was emplaced in the Qitan complex, and peralkaline magmas were intruded as dikes and extruded as rhyolite and tuff (Humaliyah formation). The Qitan complex and its environs may have potential for tin, tungsten, and(or) base metals.