Understanding how geologists conduct fieldwork through analysis of problem solving has significant potential impact on field instruction methods within geology and other science fields. Recent work has highlighted many aspects of fieldwork, but the problem solving behaviors displayed by geologists during fieldwork and the associated cognitive processes remain poorly understood. We present research showing how geology students initiate and develop geologic models as part of the problem solving process. We qualitatively analyzed field notes and interview data from 36 undergraduate geoscientists engaged in field exams during a 6-week advanced field camp. Eight cognitive approaches grouped in two broad categories emerged from the data that show how students develop geologic models. Students employ both single and multiple model approaches with varying degrees of success and frequency. The success of any given approach appears to be dependent on the level of students' geologic situation awareness. The development of multiple geologic models leads to a higher rate of success in general, because of the inherent flexibility to accommodate newly collected data. Instructors should continue to teach a multiple model approach until students have the proper geologic skills to ensure a high level of situation awareness and exhibit expert characteristics in the field. Furthermore, students should be instructed to eliminate weaker models as they progress throughout each mapping assignment.