This lab project is in two parts. In the first part students are given a map of Snake River Plain volcanic centers with a range of dates of eruptions. Based on what they know about hot-spot tracks, they use the map and reported isotopic ages to calculate a range of values for the relative velocities of the North American Plate and the Yellowstone hot spot. In the second part, students are given a map of the distribution of a volcanic ash from the Yellowstone volcanic field, with thickness of the ash where known. Students are asked to contour the map to show how the ash is distributed, and think about the factors that affect that thickness, both during and after the eruption. In both parts of the lab students have to deal with real data that is incomplete in some cases, and usually occurs as a range of values. Students must make decisions about how to treat incomplete data sets that do not have absolute values.