The Santiago Creek watershed occupies much of the northwestern end of the Santa Ana Mountains, and is located generally north of the city of Irvine.
It is bounded on the south by the San Diego Creek, Aliso Creek and Oso Creek drainage areas,  on the southeast by the Trabuco Creek watershed, and on the north and west by tributaries of the Santa Ana River.
At 100.6 square miles (261 km²) in size, the Santiago Creek watershed makes up about 3.6% of the entire 2,400-square-mile (6,200 km²) Santa Ana River watershed - but makes up about 65.7% of the 153.2 square miles (397 km²) of Santa Ana River watershed within Orange County, and 10.6% of 948-square-mile (2,460 km²) Orange County.
Most of the watershed is unincorporated, but about a third lies within Anaheim, Villa Park, Orange, and Santa Ana.

Elevations in the watershed range from 5,687 feet (1,733 m) at Santiago Peak to 108 feet (33 m) at the Santa Ana River confluence.
Although only tiny parts of the Santiago Creek watershed do not lie within Orange County, it closely borders Riverside and San Bernardino counties.
The Santa Ana Mountains rise higher on the right bank of the creek (the north bank) than on the left (south) bank, and parts of the northernmost course of the creek run through the  Puente Hills.

The major tributary watersheds, in order of their appearance from southeast to northwest (roughly in downstream order) are: Harding Canyon, Williams Canyon, Silverado Canyon, Ladd Canyon (tributary of Silverado Canyon), Baker Canyon, Black Star Canyon, Fremont Canyon, Blind Canyon, and Weir Canyon on the right bank; and Limestone Canyon and Handy Creek on the left bank.
Of the right bank tributaries, the Silverado Canyon, Ladd Canyon and Fremont Canyon sub-watersheds each extend a little into Riverside County.
The Silverado/Ladd Canyon subwatershed is the largest, and Williams Canyon is the smallest.
The Santiago Creek watershed occupies much of the northwestern end of the Santa Ana Mountains, and is located generally north of the city of Irvine. It is bounded on the south by the San Diego Creek, Aliso Creek and Oso Creek drainage areas,  on the southeast by the Trabuco Creek watershed, and on the north and west by tributaries of the Santa Ana River. At 100.6 square miles (261 km²) in size, the Santiago Creek watershed makes up about 3.6% of the entire 2,400-square-mile (6,200 km²) Santa Ana River watershed - but makes up about 65.7% of the 153.2 square miles (397 km²) of Santa Ana River watershed within Orange County, and 10.6% of 948-square-mile (2,460 km²) Orange County. Most of the watershed is unincorporated, but about a third lies within Anaheim, Villa Park, Orange, and Santa Ana.
Elevations in the watershed range from 5,687 feet (1,733 m) at Santiago Peak to 108 feet (33 m) at the Santa Ana River confluence. Although only tiny parts of the Santiago Creek watershed do not lie within Orange County, it closely borders Riverside and San Bernardino counties. The Santa Ana Mountains rise higher on the right bank of the creek (the north bank) than on the left (south) bank, and parts of the northernmost course of the creek run through the  Puente Hills.
The major tributary watersheds, in order of their appearance from southeast to northwest (roughly in downstream order) are: Harding Canyon, Williams Canyon, Silverado Canyon, Ladd Canyon (tributary of Silverado Canyon), Baker Canyon, Black Star Canyon, Fremont Canyon, Blind Canyon, and Weir Canyon on the right bank; and Limestone Canyon and Handy Creek on the left bank. Of the right bank tributaries, the Silverado Canyon, Ladd Canyon and Fremont Canyon sub-watersheds each extend a little into Riverside County. The Silverado/Ladd Canyon subwatershed is the largest, and Williams Canyon is the smallest.
Santiago Creek