Hahamongna is the rare spot in the Arroyo Seco at the foot of the San Gabriel Mountains where the mountainous watershed meets the urban plain. Periodically floods roar into this basin. Bounded on the north by the mountains and Jet Propulsion Laboratory and on the south by Devil's Gate Dam, Hahamongna contains five unique habitat zones that only exist in alluvial canyons near the mountains. Most sites like this in Southern California have been destroyed.

Don't let Hahamongna go the way of other lost environmental treasures in Southern California.

The Meaning of Hahamongna

The original settlers of the region were sometimes called the Hahamongna Indians. The word means "Flowing Waters, Fruitful Valley" in the native Tongva language.

LCF's Role in Hahamongna

Twenty years ago the City of La Cañada Flintridge played a key role in establishing Hahamongna Watershed Park and transforming the Hahamongna basin. Then City Councilmember Carol Liu (now state senator) represented LCF on the joint powers planning authority that established Hahamongna Watershed Park after LA County abandoned Oak Grove Park, which had been a County facility for many years.

LCF Impacts

  • 425 trucks per day

  • Massive air pollution from dust and diesel trucks

  • Closed recreational trails for hikers and horses

  • Seven schools in immediate area

  • Permanent scarring of 50 acres of precious stream habitat

Here's Hahamogna in the LCF Outlook

The La Cañada High Track Team Loves to Run in Hahamongna

. . . But Not After the Trucks Come

Diesel Exhaust


Initial LCF Traffic Assessment


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The View from La Cañada Flintridge


Los Angeles County is now planning a mammoth project to remove 2.4 million cubic feet of sediment from Devil's Gate Dam and haul it to Irwindale and Azusa.

The program, which was approved by the County Supervisors in November 2014, will cost $100 million and include:

  • 425 diesel trucks each day for consecutive years beginning in the fall of 2011.

  • 50,000 truckloads through the streets of our community per years; 150,000 total

  • Permanent destruction of prime riparian habitat in 50 acres of the most environmental sensitive zone of the Arroyo Seco.

  • Construction of two permanent 30 foot wide road down near the dam down into the Hahamongna basin.

  • Massive air quality impacts from the dust and diesel funds collecting in the Hahamongna basin at the western edge of La Cañada.

When the Flood Control District originally announced a sediment reduction program after the Station Fire in 2009, they intended to conduct the project without any environmental review, community concerns about its scale and impacts led the County Supervisors to instruct staff to prepare a full environmental impact report, which the are now doing. The plan then was to remove 1.6 million cubic yards of sand and sediment from the basin at a projected cost of $34 million, but by the time they finished the environmental impact report, the amount to be removed has increased along with the cost and impacts to our neighborhoods.

There are many concerned citizens and a coalition of organizations who believe this project is too massive and should scaled back significantly. For example, an ongoing program of sediment removal and using flood flows to remove sediment can effectively manage the flood basin and preserve habitat. The La Cañada City Council considered the impacts at several meetings. The Pasadena City Council established a Sediment Working Group of experts and stakeholders to develop a more sustainable approached and unanimously endorsed the recommendations of that group which would reduce the impacts on our neighborhoods to about one quarter of the County's program. There are other ways to manage the basin in a more environmentally sensitive manner, but the County does not seem to have taken them seriously. For that reason, the Arroyo Seco Foundation and the Pasadena Audubon Society filed a lawsuiting the County Flood Control District's Environmental Impact Report on December 11, 2014.

Pasadena, La Cañada Flintridge, and Altadena all have a great deal at stake and need to take the lead in insisting that the County develop a more environmentally sensitive plan, but this is an issue that affects many other regions in Southern California. A new paradigm for flood management is need that does not just rely on concrete and trucks. This should be a widely discussed issue in the upcoming municipal elections in Pasadena and La Cañada. Only public pressure, regulatory hammers and litigation can ensure a more sensible and sensitive management plan.

We urge you and local organizations to get involved and support the lawsuit to protect Hahamongna and our neighborhoods.