arroyo hondo means "deep creek" in spanish. its isabel creek tributary is significant in that the spanish name for mt. hamilton was the "sierra de santa isabel", and the highest point was then referred to as mount isabel instead of mount hamilton. when william henry brewer and charles hoffman of the whitney survey climbed the peak on august 26, 1861, they did not know it had a name, and christened it mt. hamilton, although they did correctly place isabel valley on their map to the east. when in 1895, the usgs realized that the peak two miles southeast of mt. hamilton was as tall (, they correctly named it mt. isabel.