This research note presents a method for using mobile device trace data to improve collection of data on spontaneously erupting protest activity and related events. Based on this method, it presents a highly granular dataset of such activity for the George Floyd Protests in the United States. We use anonymous aggregated mobile device trace data to identify device surges: anomalous changes in the number of devices in a small geographic area, consistent with the assembly of a large number of individuals. Preliminary estimates from ongoing data collection of protest sites and scale are presented. Establishing better measures of where and when protests occur across and within cities improves researchers' understanding of the downstream political and social consequences of mobilization.