The creek is named for Francisco Pacheco and Juan P. Pacheco who were granted the Rancho Ausaymas y San Felipeland grants in 1833 and 1836, and 1843 respectively. Francisco Pacheco came to California in 1819. Just north of the earthen dam on North Fork Pacheco Creek was one of the last refuges of the Amah-Mutsun band of the Ohlone people, and is rich archeologically with multiple burial sites and artifacts, including projective points so large that they would have been used for bear or elk. In 1993, Mark Hylkema documented eight different Native American sites in this area, dating from 1000 B.C. to 500 A.D.
Flooding
On 11 January 2017, a levee break at Pacheco Creek affected fifty local homes; some homes had mudlines about five feet high. On 12 January, health officials advised some local residents not to drink local tapwater pending contamination testing.
Watershed
The mainstem Pacheco Creek is formed by the confluence of the North Fork Pacheco Creek and South Fork Pacheco Creek about west of Pacheco Pass. The creek generally follows Highway 152, passing from Santa Clara County to San Benito County, and continuing until it empties into San Felipe Lake, the source of the Pajaro River. The North Fork Pacheco Creek is a stream beginning in Henry W. Coe State Park at and receives the East Fork Pacheco Creek, at Chimney Rock before reaching Pacheco Reservoir, the latter just north of Highway 152 and the confluence of North and South Forks Pacheco Creek. The Mississippi Creek tributary of North Fork Pacheco Creek is has an impoundment above elevation, and sources on Bear Mountain on the northern side of Henry W. Coe State Park. Just before joining Pacheco Creek above San Felipe Lake, it is joined by Tequisquita Slough. The latter has 3 main tributaries, Santa Ana Creek, Arroyo de Los Viboras, and Arroyo Dos Pichachos. Santa Ana Creek is apparently named for the Rancho Santa Ana y Quien Sabeland grant. Stream flow in Pacheco Creek is influenced by releases from the North Fork Pacheco Reservoir, which is operated by the Pacheco Pass Water District.
Ecology
Significant remnants of the historic riparian California sycamore habitat still exists on Pacheco Creek and are a good example of the Central CoastSycamore Alluvial Woodland habitat type. Pacheco Creek historically hosted steelhead trout as evidenced by a physical specimen collected in 1945 by D.H. Simpson in the California Academy of Sciences, "19.5 miles east of Gilroy on Hwy. 152". Pacheco Reservoir is an impassable barrier to in-migrating steelhead trout, preventing access to the nearly of stream consisting of North Fork Pacheco Creek, Mississippi Creek and East Fork Pacheco Creek. In addition, resident rainbow successfully rear in fast-water habitats grow rapidly and reach smolt size by the end of their first summer. In many years in late spring, prior to reservoir releases for agriculture, low stream flows and high water temperatures severely impact steelhead fry and small juveniles. Other native fish in North Fork Pacheco Creek include Monterey sucker and Sacramento pikeminnow.
