Rivers are important surficial geologic processes that shape Earth's landscape. Students' conceptions of river features and processes serve as a foundation for their learning of new river concepts. Despite the importance of rivers and students' conceptions of them, little research has focused on identifying students' river conceptions. This study investigated students' conceptions of the role of river processes in canyon formation. In-depth interviews with 18 college students were conducted, and students' responses were analyzed using a modified version of constant comparative analysis. Students' conceptions fell into three categories: incomplete scientific conceptions, alternative conceptions, and incomplete scientific-alternative conceptions. Students with incomplete scientific conceptions thought that rivers carved canyons and did not recognize the connection between surficial processes and base level changes in forming a canyon. Students with alternative conceptions thought that catastrophic processes such as earthquakes form canyons or that canyons do not undergo a formation process at all (i.e., they have always been there). Students with incomplete scientific-alternative conceptions thought that catastrophic processes initiated canyon formation (similar to those students who held alternative conceptions) but also thought that rivers contributed to the process of canyon formation (similar to those students who held incomplete scientific conceptions). These findings add to the growing knowledge base of geoscience conceptions and have implications for improving geoscience teaching strategies.