Restricted to geophysics majors. Field studies for geophysics majors, including seismic, magnetic, electrical, gravity, and other techniques; related data processing and interpretation. Each half requires three consecutive weeks of fieldwork. Geological Sciences 661A is offered either between the spring semester and the summer session or in the summer session; Geological Sciences 661B is offered in the summer session. Students may take Geological Sciences 661 for University credit while enrolled in the Los Alamos National Laboratory SAGE program. May be used in place of Geological Sciences 660 to fulfill the requirements for the Bachelor of Science in Geological Sciences (Option II: Geophysics). Prerequisite: Geological Sciences 420K, 465K, and 365P with a grade of at least C- in each.