The Spanish name for Mt. Hamilton was the Sierra de Santa Isabel and the highest point was originally known as Mount Isabel instead of Mount Hamilton. William Henry Brewer and his fellow geologist, Charles F. Hoffmann, did not know it already had a name, and named it Mt. Hamilton, although they did place Isabel Valley on their map to the east. The Hotel Santa Ysabel was built on the road up the mountain in 1885 on Smith Creek. When in 1895, the USGS realized that the peak two miles southeast of Mt. Hamilton was as tall (), they named it Mt. Isabel.