Many standards documents and learning progressions recommend evolution learning in elementary grades. Given young children's interest in dinosaurs and other fossils, fossil investigations can provide a rich entry into evolutionary biology for young learners. Educational psychology literature has addressed children's reasoning about foundational concepts related to fossils such as living/nonliving distinctions, causation, origins of objects, and conceptions of time. This exploratory qualitative case study explored preschool children's ideas about fossils and these foundational concepts as children moved through a 1-week science camp devoted to fossils. Research participants consisted of 15 preschool children aged 3-6 enrolled in a university-affiliated summer camp. Data sources included daily assessments and postcamp individual interviews. Data analysis yielded several main findings. Children were successful at determining where fossils could be found, identifying familiar fossils and fossil tracks, ascertaining that familiar and unfamiliar fossils were nonliving, and determining that rocks have natural origins. Children struggled more often at understanding how fossils differ from recent bones and skulls, properties uniting fossils, and the natural origins of plants and unfamiliar fossils. We also noted clear age- and object-related trends for living/nonliving distinctions, teleological reasoning, origins, and object ages. Implications for future research and practice are offered.