Model has been constructed from magnetic, gravity and seismic data from EL 370 (Aquitaine and Delhi), of a shallow horst of granitoid basement in the southeast of Yadlamalka 1:50 000 area, and, under the lake, a basin, up to 4 500 metres of dense sediments, overlain by 1 600 metres of shelf sediments, which are faulted. Shallow graben filled with ?Tertiary sediments is suggested and areas of possible Cambrian sedimentation are shown. To the east of Wilga Point cylindrical pipe of magnetic material occurs at a depth which suggests vent from which the Beda Volcanics may have been extruded. This and 2 smaller coincident magnetic and gravity anomalies warrant further work.