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{{Short description|Creek in Central California}}
{{Infobox river
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| municipality =
| city = [[San Ramon, CA]]
| length = 6.72 miles<ref>{{Cite web |date=2004 |title=Contra Costa County Creeks Inventory |url=http://www.cccleanwater.org/_pdfs/Creeks_Inventory.pdf
|website=www.cccleanwater.org}}</ref>
| length_round =
| source =
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| source_country =
| mouth = [[San Ramon Creek]]
| mouth_coordinates = {{coord|37.77085|-121.98988|format=dms|type:river_region:US-CA|display=inline,title}}
| mouth_country =
| discharge_location =
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| discharge_round =
| website =
| river_system = [[Walnut Creek
}}
'''Bollinger Canyon Creek''' is an approximately 6.72
== Course ==
Bollinger Canyon Creek begins as a number of [[ephemeral stream]]s emitting from a [[Horst (geology)|horst]] valley, Bollinger Canyon, in the highest reaches of the [[Berkeley Hills]], in California's [[Inner Coast Ranges]].<ref name=":1" />
The highest point in the drainage is around 2,000 feet above sea level.<ref name=":0" /> From a low divide which separates it with [[Las Trampas Creek]], it runs southward through Bollinger Canyon, gradually descending in altitude until turning sharply to the east near Crow Canyon Road in [[San Ramon, California]]. It is joined by its only named tributary, San Catanio Creek. Shortly after, it is confined to concrete channels and it joins with San Ramon Creek near the city's downtown.<ref name=":3">{{Cite web |last=Leidy |first=Robert A. |date=2005 |title=Historical Distribution and Current Status of Steelhead/Rainbow Trout (Oncorhynchus mykiss) in Streams of the San Francisco Estuary, California |url=http://www.cemar.org/pdf/wholedoc2.pdf}}</ref>
File:Fog moves up Bollinger Canyon.png|link=|Fog rolling up Bollinger Canyon to the divide between Bollinger Creek and [[Las Trampas Creek]] (December 19, 2021)▼
== Geography ==
Bollinger Creek exhibits a character similar to many other streams in [[Central California]]. It is vegetated with [[California mixed evergreen forest]], [[chaparral]] and open grasslands, habitats typical of the [[East Bay]] region. Many of its tributaries only carry water during storms.[[File:Bollinger Canyon Creek Tributary.jpg|thumb|One of the many small tributaries flowing out of the walls of Bollinger Canyon into Bollinger Creek. (December 19th, 2021)|left]]
The region surrounding the creek has a [[cool-summer mediterranean]] climate which generally keeps temperatures mild.<ref>{{Cite web |date=1977 |title=Mean Seasonal Isohyets compiled from precipitation records |url=https://www.contracosta.ca.gov/DocumentCenter/View/770/CCCo-Isohyet-Map-Low-Color-PDF?bidId= |website=www.contracosta.ca.gov}}</ref> Due to its proximity to the [[Pacific Ocean]], the creek and its watershed are often inundated with fog.
Virtually the entirety of the creek's course upstream from [[San Ramon, California]] is undeveloped, with ranching and open space making up the majority of land use.<ref name=":0" />
Bollinger Creek's headwaters lie in [[EBRPD]]'s [[Las Trampas Regional Wilderness]], which is a popular area among locals for hiking, biking, birding and geology. The park features a number of hiking and biking paths that traverse Bollinger Canyon, [[Rocky Ridge, California|Rocky Ridge]] and [[Las Trampas Ridge]].
The porous formations of [[Briones Sandstone]] that comprise the canyon walls trap rainfall and aid the formation of the numerous springs that feed the creek.<ref name=":1">{{Cite web |last=Knight |first=Walter |date=1978 |title=The Story of Las Trampas |url=https://www.ebparks.org/sites/default/files/lastrampas_the_story.pdf |website=www.ebparks.org}}</ref>
== Ecology ==
▲[[File:Fog moves up Bollinger Canyon.png|
[[File:Bollinger Canyon and Bollinger Creek with Mt. Diablo in the background.jpg|left|thumb|Late spring in Bollinger Canyon from [[Rocky Ridge, California|Rocky Ridge]]; Bollinger Creek runs through a belt of oak and laurel trees with Las Trampas Ridge and [[Mount Diablo]] in the background. (May 24th, 2022)]]
Because much of its course is undeveloped, Bollinger Creek is an important habitat for local wildlife. Much of the land in the watershed is forested and rugged, providing habitat for a variety of wildlife species. [[Black-tailed deer]], [[Coyote]] and [[Wild boar|boar]] are seen regularly.<ref name=":4">{{Cite web |date=2024-01-28 |title=Las Trampas Wilderness Regional Preserve |url=https://www.ebparks.org/parks/las-trampas |access-date=2023-11-22 |website=East Bay Parks |language=en}}</ref>
A wide variety of raptors, among them [[Red-shouldered hawk|Red-shouldered hawks]] and [[Great horned owl|Great horned owls]] reside in the watershed, particularly on the steep rock outcrops on Las Trampas Ridge, as well as [[Turkey vulture|turkey vultures]].<ref name=":4" />
=== Trout Population ===
Bollinger Canyon Creek is unique in that it retains a population of [[Coastal rainbow trout]] which have been extirpated from much of the [[San Francisco Bay]] watershed through development and the installation of migration barriers like dams.<ref name=":2" /> It is speculated that this population is of hatchery origin and escaped from a stocked pond during a flood event.<ref name=":3" /> Regardless of their origin, the most recent survey of trout distribution in the region showed that rainbow trout were successfully reproducing in Bollinger Creek.<ref name=":3" /> The lack of development in Bollinger Canyon and the quality of the habitat found in the area has likely aided the trouts' establishment in the creek. The total population is unknown, and it is unclear how the trout fared during the severe [[Droughts in California|droughts]] between 2012 and 2020.
== References ==
{{reflist}}
[[Category:Rivers of California]]
[[Category:Contra Costa County, California]]
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