To study the role of spatial concepts in science learning, 125 college students with high, medium, or low scores on a horizontality (water-level) spatial task were given information about geological strike and dip using existing educational materials. Participants mapped an outcrop's strike and dip, a rod's orientation, pointed to a distant building and north, and completed 3-dimensional horizontality and verticality tasks. Many students, particularly those with low water-level scores, experienced difficulty on both field and laboratory tasks and failed to use good field-observation strategies. Error patterns implicated roles of cognitive regularization of the environment, embodied spatial cognition, and map experience. Data relating performance to participants' spatial skills, gender, self-reported confidence in responses, spatial awareness, and strategy use suggest a range of instructional approaches. (Contains 3 tables, 5 footnotes and 14 figures.)