We present a mixed-methods approach to community-based assessment design that engages tribal college and university faculty, students, and science educators, as well as experts in cultural knowledge from the Blackfeet and Diné (Navajo) nations. Information from cultural experts, gathered through a combination of sequential surveys and focus group sessions, was analyzed to identify important themes with regard to assessment and geoscience content within the context of these communities. While experts use a variety of assessment approaches in their classrooms, only pre- and posttesting and portfolios were found to be most valuable. Experts indicated that the primary role of assessment was to monitor student progress, steer instruction, and prepare students for success; thus, assessment should be tied to the course goals. Experts differed on their views regarding sources of bias in testing, but overall they agreed that test language and content were both strong sources of bias. They indicated that input on assessment would help to incorporate local context and provide a mechanism for combating bias. Surveys completed by tribal college faculty and Native American students from Blackfeet Community College (BCC) and Arizona State University (ASU) provided information on the themes of geoscience, native science, place, and culture. Participants provided a variety of examples of important geoscience concepts that focused on (1) traditional geoscience concepts (e.g., the composition of Earth materials), (2) Earth system concepts (e.g., the environment and ecosystems), and (3) interactions between native culture and geoscience (e.g., incorporation of native language in science curriculum). Combined, these data offer the basis for developing place-based and culturally informed geoscience assessments by revealing geoscience content that is important to the local community. To aid in assessment design, one-on-one interviews with tribal college faculty and science educators, as well as students from BCC and ASU, provided specific feedback on the question validity of select items from an existing instrument: the Geoscience Concept Inventory (GCI). Emergent themes from the interview transcripts address assessment content, language, and format and reference school science, cultural knowledge, physical places, and connections to the local landscape (e.g., sense of place). Together, these data (1) address the validity of the GCI as a standardized assessment measure in these student populations and (2) provide the basis for developing open-ended assessment questions and concept inventory-like questions that incorporate this feedback.