Natural source (MT) and controlled source audiomagnetotellurics (CSAMT) surveys have been conducted in the Illinois Valley, near Cave Junction, Oregon, USA. The primary objectives of the investigation were to characterize local aquifers, determine the thickness of alluvium and assist in the future sighting of high production irrigation wells. A total of 58 stations were occupied providing 3.25 km of nearly continuous resistivity-depth profiles. Combining information found in well logs and resistivity data indicated the locations of more resistive coarse grain alluvial aquifers with resistivity ranging from 25 to 100 ohm-m interlayered by less resistive clay rich alluvial layers (1-25 ohm-m). Alluvium thickness estimates range from 35 to >250m in area studied.