Seismic reflection surveys of the Great Salt Lake, Utah, have provided continuous profiles for more than 750 km (450 mi) using air-gun and sparker sources. Useful penetration to as much as 1,220 m (4,000 ft) has been obtained in an average water depth of 6 m (20 ft). The data were deconvolved, processed, and displayed using a computer graphics system. In addition, a total-field aeromagnetic survey, flown at a terrain clearance of 152 m (500 ft), provided 750 km (450 mi) of corresponding profile coverage. Interpretation of the seismic data indicates that the Tertiary and Quaternary sediments of the Great Salt Lake were deposited in north-trending basins characterized by gently east-dipping beds over most of the west and central areas. Rapid subsidence and secondary folding occurred adjacent to north-trending normal fault zones along the east side of the lake. Buried anticlines and faults along the east side suggest a pre–late Tertiary period of deformation characterized by normal faulting and basin development. The total thickness of Tertiary and Quaternary sediments ranges from ∼488 m (1,600 ft) in the north to more than 3,658 m (10,000 ft) in the south. The Quaternary sediments alone range in thickness from at least 152 m (500 ft) in the north to more than 396 m (1,300 ft) in the south. Interbedded volcanic rocks, probably basalt of late Tertiary age, occur as shallow flows beneath the northern portion of the lake. West of Promontory Point, restricted basins of Quaternary origin contain ∼8 m (25 ft) of unconsolidated mud and silt overlying 213 m (700 ft) of inter-bedded mirabilite, silt, and clay. In several locations along the causeway, the mirabilite has flowed into near-surface diapiric folds and small domes. This sequence suggests restricted deposition during cool climate near the end of Pleistocene time, followed by a rapid increase in mean annual temperature with widespread deposition of mud and clay.