The Las Trampas Creek Basin is a tapestry of rural, suburban and urban lands; its highest reaches remaining relatively pristine in appearance aside from the intrusions of cattle ranching, hiking paths and a single road.

[2] Rugged slopes draped in Chaparral, California oak woodland and invasive annual grassland with small forested valleys in between define the watercourse.

Downstream from present Saint Mary's College in Moraga, CA essentially all the way to its confluence with Walnut Creek, Las Trampas Creek coursed through a wide and undulating valley floor near the community of Burton Valley with deep soil, it spread its waters out across a broad floodplain in times of excess flow, and retained water only in pools during times of drought.

Like in other places in arid western North America, the beaver probably played a crucial role in retaining water through the dry season and providing habitat for fish and wildlife.

Accounts of the region from Spanish and Mexican times (1769 to 1848) speak of large herds of tule elk inhabiting the hills and valleys that would have no doubt taken advantage of the fertile grazing lands and watering holes provided by Las Trampas Creek.

[8] The demand for agricultural land throughout the late 19th and early 20th centuries led landowners to clear the forests and savannas of oak trees that filled the valley bottoms along Las Trampas Creek to plant grain fields.

[7] In the wake of a series of major floods in the 1950s and 60s, urban planners in the growing cities surrounding the watershed, with the help of the government, decided to channelize much of Las Trampas creek.

Springs that emerge from the rock rush down the numerous gulleys that line the walls of the upper Las Trampas Creek canyon, feeding the stream.

The human history of the Las Trampas Creek watershed began thousands of years ago when groups of Paleo-Indians made their way into the Bay Area.

A series of epidemics among the natives of the interior coupled with a drought in the 1790s forced many Saclan to seek refuge at Mission Dolores across the Bay on the San Francisco Peninsula.

By about 1806, after years of disease, ecological and social collapse and raids from the Spanish military, the Las Trampas creek watershed and the rest of the Saclan homeland was all but devoid of people.

In the early 1900s, construction at Saint Mary's College required a reliable water source, and so Las Trampas Creek was dammed near the mouth of Bollinger Canyon to create Lake Lasalle.

[14] Beginning the 1930s, but greatly expanding during the post World War II housing boom, suburban communities were built along much of the creek, replacing orchards and pastures.