Mathematical modeling, a practice standard in the Common Core State Standards for Mathematics (CCSSM) (CCSSI 2010), is a process by which students develop and use mathematics as a tool to make sense of the world around them. Students investigate a real-world situation by asking mathematical questions; along the way, they need to decide how to use appropriate tools and mathematical content knowledge. After devising a solution, students interpret their model to determine if it makes sense and if it can be modified. The practice of mathematical modeling is of growing importance in mathematics education because it bolsters mathematical proficiencies beyond traditional content knowledge. Modeling tasks are distinct from many other mathematical activities because of their openness. Instead of being presented with a specific mathematical problem, students are presented with a situation and allowed to problem pose to determine what mathematical questions might be appropriate to ask. With the 2016 national park centennial and such initiatives as Find Your Park, students and teachers alike are encouraged to explore state and national parks as their outdoor classrooms. From terrain change to average daily temperature, many aspects of the outdoors can be explored through mathematics. Because of their location, several fifth-grade classrooms have the opportunity to visit Yellowstone National Park. Exploring Yellowstone is both relevant and motivating for students because most have already visited or learned about some features of the park. For these reasons, as teachers, the authors thought that Yellowstone could act as an ideal context in which to investigate measurement topics and engage in the process of mathematical modeling. This article presents how using maps as part of a measurement activity engaged fifth graders as they studied the area of a Yellowstone National Park. (A bibliography is included.)