Community-based research models hold potential to change who conducts geoscience research, its relevance to the public, and how researchers may begin to address historical injustices. However, this potential is contingent on such projects being led in ways that meaningfully and equitably bridge the worlds of scientists and community stakeholders. Here, we present an in-depth, comparative case study of leadership in two place-based, community-based projects funded through an NSF initiative. Primarily focusing on two Principal Investigators, we draw data from participant interviews, journal entries, and project observations over fourteen months. One project is centered at an urban watercress farm in Hawai'i and one is centered on the Los Angeles River in California. We use theories of symbolic boundaries and methods of comparative case study to identify leadership practices that facilitate successful place-based, community-based research involving scientists and members of historically excluded communities. We find boundary-spanning leadership to include a critical awareness of scientific history, efforts to center community at all phases of the work, and trust-building practices that strengthen confidence in the team. This work carries theoretical implications for geoscientists working across politicized differences, practical implications for leadership development, and structural implications for the incentives and design of community-based scholarship. We hypothesize community-based science could increase the perceived social and cultural relevance of geosciences, and thereby broaden participation and reduce inequities in who contributes knowledge to these fields.