Rocky Brook is the second largest tributary to the Dosewallips River after Silt Creek, draining an area of about 8.5 square miles and ranging from about 600 feet above sea level up to around 4200 feet or so. The basin receives heavy rain throughout the year, and a not insignificant amount of snow in the winter, so despite not having a terribly large basin the creek flows well all year long. This factor, plus the considerable height of the falls likely spurred the installation of a hydroelectric facility at the falls in 1986. Fortunately the falls are allowed to flow year round, and even with the diversion can still swell to an impressive volume after periods of heavy rain.