Collaborative human-robot field operations rely on timely decision-making and coordination, which can be challenging for heterogeneous teams operating in large-scale deployments. In this work, we present the design of an immersive, mixed reality (MR) interface to support sense-making and situational awareness based on the data collection capabilities of both human and robotic team members. Our solution integrates state-of-the-art methods in environment mapping and MR so that users may gain rapid insights regarding the working environment, the current and previous locations of human and robot team members, and the environment data such team members have collected. We describe the implementation of our system, share lessons learned in collaborating with emergency responders throughout our design process, and offer a vision for the use of immersive displays for human-robot field team deployments in large-scale outdoor environments.