Granular-surfaced roads comprise 73% of Iowa’s county road network. The surfaces of these gravel roads undergo mechanical and chemical deterioration over time due to extreme weather conditions and traffic loads. The goal of the present study is to improve our understanding of the mechanical deterioration that affects the performance of different geological types of coarse aggregates used in granular roads and shoulders. Samples of coarse aggregates were collected from four different quarries in Iowa. Laboratory gyratory compaction tests (GCT) were performed on specimens of the quarry samples to simulate their degradation under traffic loading conditions over time. From the results of GCTs, breakage parameters are evaluated, and relationships between dry unit weight, shear strength, and compaction energy are established for the different aggregate types examined. From these relationships, an efficient field-compaction energy criterion is determined to maximize density and shear strength while minimizing over-compaction and breakage of the aggregates.