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.

The La Cañada High Track Team Loves to Run in Hahamongna

. . . But Not After the Trucks Come

Diesel Exhaust


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The View from La Cañada Flintridge


Los Angeles County is now planning a mammoth project to remove 1.6 million cubic feet of sediment from Devil's Gate Dam and haul it to Irwindale and Azusa. Although the Flood Control District originally 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 proposed program will cost $35 million and include:

  • Three to four hundred diesel trucks each day for seven months for three consecutive years beginning in the fall of 2011.

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

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

There are many concerned citizens and a coalition of organizations that believe this project is too massive, and could scaled back significantly. 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 example, an ongoing program of sediment removal and using flood flows to remove sediment can effectively manage the flood basin and preserve habitat. An environmental review would have forced consideration that and other alternatives, but the County's reliance on an emergency declaration will deny the public that analysis.

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. This should be a widely discussed issue in the upcoming municipal elections in Pasadena and La Cañada. Only public pressure, regulatory hammers and litigation if necessary can ensure a more sensible and sensitive management plan.

Proposal to City Council of La Cañada by LA County Supervisor Michael Antonovich

Upon request, Erik Zandvliet, the City Traffic Engineer, provided the minutes of the January 19, 2011 Special meeting of the La Cañada City Council.

Yesterday, the Council was informed about an upcoming County project to clear debris from the Hahamonga park basin, aka "Devil's Gate Reservoir".

Here is an excerpt of the project description given by LA County Flood Control District:

"Los Angeles County Flood Control District is currently working on a major sediment removal project from Devil's Gate Reservoir. Although the excavation site is in the City of Pasadena, we will need to utilize roads belonging to the City of La Cañada Flintridge to haul material to the disposal site in the Cities of Azusa and Irwindale. We are planning to haul a total of 1,671,000 CY (cubic yards) of post fire debris over a 3-year span. Work on this project is expected to begin September 2011. Subsequently excavation will begin as early as May and end as late as December of each year, weather permitting. Work will only ensue Monday-Friday from 7:30am to 5:00pm.

The inbound haul route will be coming northbound on the 210 and exiting at Berkshire Place, making a right onto Oak Grove Drive and then a left into the construction site. The outbound haul route will exit the construction site heading north on Oak Grove Drive, making a left on Berkshire Place and then another left onto the 210 southbound. Both inbound and outbound traffic will venture near the south end of La Cañada High School."

This translates to about 170,000 truck trips. The route would NOT go past the front of La Cañada High School. We have informed LAC-FCD that we are asking for the street pavement to be replaced at the end of the project, and that we would have to approve a hauling plan that avoids school times and JPL peak hours. They have agreed in principal to these conditions. We have also asked the County to consider splitting the trips onto other streets as well.