The Wadi Shuqub quadrangle (sheet 20/41 A) lies in the high mountainous part of the Hijaz plateau in west-central Saudi Arabia. The quadrangle is underlain chiefly by Precambrian layered metasedimentary and metavolcanic rocks that are intruded by plutons ranging in composition from gabbroic to granitic. The metasedimentary rocks include quartzite, phyllitic quartzite, phyllite, slate, argillite, granulite, schist, and marble. The metavolcanic rocks are mostly greenstone and greenstone tuff but include meta-andesite and metadacite. The rocks are in the greenschist and greenschist-amphibolite transition facies. The major plutonic rocks are tonalite and quartz diorite, which form a large batholith in the western part of the quadrangle. Smaller bodies of diorite and gabbro, granite, and complexes of mixed rocks are also present. The layered rocks are divided into sixunits that have been described in outcrop order, from east to west: 1) nearly all greenstone, 2) mixed metasedimentary and metavolcanic rocks, 3) nearly all metasedimentary rocks, 4) greenstone in eastern part, metasedimentary and metavolcanic rocks in western part, 5) nearly all metasedimentary rocks, and 6) metavolcanic rocks containing subordinate amounts of metasedimentary rocks. The layered rocks have a northerly strike throughout the quadrangle except near the southwest corner where they strike northwest. The rocks are steeply dipping to vertical. Major deformation has produced isoclinal folds and shears, strike faults, and subordinate cross faults. A second stage of deformation resulted in local open folds. Basalt of Quaternary age covers the Precambrian rocks near the eastern margin of the quadrangle, and alluvium underlies major wadis and flats. The main part of the Wadi Bidah mining district, including at least four ancient mining sites, is in the southeast part of the quadrangle. The district has produced gold from gold-quartz veins, and has some potential for producing, gold, silver, copper, zinc, and lead from massive sulfide deposits.