The steady state exists in a system of fans when all of the fans are increasing in thickness at approximately the same rate. Laboratory and field observations suggest that the steady-state slope of an alluvial fan is determined by debris size, depositional process, and water discharge. Large fans have larger drainage basins and hence larger discharges than small fans. Consequently, fan slope generally decreases with increasing fan area. Under otherwise equivalent conditions, fans composed of coarse material are steeper than those composed of fine material, and fans built largely by debris flows or sieve deposition are steeper than fans on which fluvial processes dominated.