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Creek Description

Big Chico Creek (Map) originates on Colby Mountain and flows 72 km to its confluence with the Sacramento River. Watershed elevation ranges from about 37 m at the mouth to 1830 m. Mean precipitation ranges from ca. 63 cm in the valley to 203 cm in the headwater region. Because of the precipitation gradient the majority of the flow of Chico Creek enters in the upper third of the drainage, making stream size relatively constant thereafter.

Like most streams, Chico Creek shows a biotic gradient from source to mouth. This gradient can be broken into three zones based largely on fish populations. Boundaries to the zones are formed partly by physiological limitations of the organisms but mostly by geological barriers. As Chico Creek carved its canyon, it cut down through tilted layers of rock to its present gradient. The harder layers, being less readily eroded, formed narrow canyons with rapids or waterfalls which tend to act as filters to upstream movement of aquatic life. The most downstream filter occurs where the creek crosses the Lovejoy basalt (Bear Hole to Brown's Hole in Bidwell Park). In this stretch, known as Iron Canyon, the valley narrows abruptly and the stream gradient increases. At its upper end, where the basalt is undercut, mass wasting has brought huge boulders into a jumble in the creek bed. This jumble of boulders acts as an impassable barrier to upstream movement of fish during normal creek flows. Under conditions of high flow, water fills in around the boulders and Iron Canyon may be no barrier at all. Steelhead, moving upstream between November and February, can usually pass the barrier. Spring-run salmon, squawfish, hardheads, and suckers, which migrate in March and April, are less likely to pass it most years. Smallmouth bass, which are inactive during the cold months, would never be expected to cross it. A fish ladder, constructed in the forties, was repaired in summer, 1993, and will require continual upkeep to function. Even with the ladder perfectly maintained, sections of Iron Canyon will remain impassable at base flow.

The next barrier begins at Higgin's Hole (about 1/3 km upstream of Ponderosa Way) where the creek begins carving harder metamorphic rock. Again the canyon narrows with big boulders, bedrock potholes, and spectacular waterfalls. In very unusual years when migration corresponded exactly with high flow, salmon or steelhead might get through this canyon to the waterfall at Bear Lake, but other fish species would never be expected to do so. The physical barriers divide Chico Creek into an upper zone from the headwaters to Higgin's Hole, a middle zone between Higgin's hole and Iron Canyon, and a lower zone between Iron Canyon and the river.

The upper zone supports only resident rainbow and brown trout. The lower zone is too warm in summer for salmonids and supports suckers, hardheads, squawfish, sculpins, smallmouth bass, and a few green sunfish. The middle zone supports all species of fish common to the lower zone (except smallmouths and sunfish) as well as populations of rainbow trout and California roach (a small, native minnow). Both middle and lower zone are used for spawning and nursery areas by anadromous lampreys and salmonids although runs of salmonids have been poor in recent years. The middle zone is crucial to survival of populations of steelhead rainbow trout and spring-run chinook salmon in the creek, since adults of the salmon and juveniles of the steelhead spend the summer in the creek. Runs of both these species had declined severely during the seventies.