Reconnaissance geologic map of the Ash Shamila quadrangle, sheet 26/40 A, Kingdom of Saudi Arabia

The Ash Shamila quadrangle, sheet 26/40 A, is centred 168 km southwest of Ha’il, in north-central Saudi Arabia, and is bounded by lat 26°30’ and 27°00’ N. and long 40°00’ and 40°30’ E. Access is by way of the Al Madihah – Ha’il paved highway to Hulayfah or Gazzalah, thence by unimproved road to Zarghat, located a few km from the eastern margin and the southeast corner of the quadrangle. Desert tracks lead from Zarghat to the remainder of the area, but a large part of the quadrangle is underlain by the Tertiary and Quaternary Harrat Ithnayn; access over this terrain by vehicle is difficult.

The area has low relief, marked only by Paleozoic sandstone remnants, volcanic cones in the harrat, and Jabal Bushra. Drainage on the harrat trends generally northerly, but rainfall is low. The climate is typical of inland Saudi Arabia, with summer day temperatures reaching 45-50°C, and with cold nights. Temperatures can reach 0°C in winter. Vegetation is sparse.

The area is sparsely populated, and permanent water is available from wells at Ash Shamila.