Hahamongna is that 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.

Witness the Winter Storms in Hahamongna

Winter 2009

December 2010 Storms

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.

July, 2010 - Council Eliminates One Soccer Field, Proceeds on Second

Council Action

Save Hahamongna is a campaign of the Arroyo Seco Foundation and other local organizations and concerned residents who are working to protect and preserve the nature of Hahamongna. We invite you to join us.

The Significance of Sediment EIR

County Supervisors on March 1, 2011 instructed County Public Works to conduct a full environmental impact report on the sediment management program at Devil's Gate Dam and Hahamongna in the Arroyo Seco.

Sups Approve EIR

Emergency Measures Completed

County crews completed the emergency measures at Devil's Gate Dam in late 2011.

Emergency Measures

View the Walkabout Videos Here

Hahamongna Walkabout 2012

Sign Up for Updates

View EIR Comments

EIR Toolkit

JPL Parking Lot To Go

JPL Parking

A New Paradigm for Sediment Management

Hahamongna Updates

More than 150,000 Trucks

La Cañada Alert

La Cañada

Dangers of Diesel


A Strategy to Save Hahamongna


Superior Court Judge Halts County Big Dig in Hahamongna

The Honorable James C. Chalfant shut down the County Flood Control's Big Dig Project for Devil's Gate Dam in Hahamongna Watershed Park. He found that the environmental impact report for the Devil's Gate Sediment Removal Project is critically flawed regarding air quality, mitigation and cumulative impacts measures. Responding to the lawsuit filed by the Arroyo Seco Foundation and Pasadena Audubon, he ordered the Flood Control District to redraft key sections of their flawed environmental impact report. After the revisions are released to the public, there will be a forty-five review period, at the end of which the County Board of Supervisors will hold a public hearing and must act to certify that the entire EIR is in compliance with the California Environmental Quality Act (CEQA).

Judge Chaltant also admonished the Flood Control District to take no further actions to further the project until they come back to him and demonstrate that they are in full environmental compliance.

Jan 2017 Update  |  February 14, 2017 Hearing  |  March 23, 2017 Hearing

Factsheet  |  Contact Supervisors

SUPS: Time for a New Look at the Big Dig

Now that there's a new Board of Supervisors who are more progressive and environmentally oriented, it time for them to take a new look at the Flood Control District's devastating plan for Hahamongna and at the unchecked power of the Flood Control District.

Candidates State Their Views on Big Dig at Hahamongna

Supervisor's Race Could Be Key to Hahamongna's Future

September 16, 2016 - The candidates to replace Supervisor Mike Antonovich addressed the County's Big Dig program for Hahamongna at a debate last night at Pasadena City College. The debate was sponsored by the League of Women Voters, Pasadena City College and the Pasadena Chamber of Commerce. The candidates responded to a question from the audience that raised concerns about the enormous impacts of the Flood Control District's sediment removal program from the Devil's Gate Dam area in Hahamongna Watershed Park.

No Big Dig Lawsuit Update

Endangered Birds Spotted in Hahamongna

The recent discovery of a pair of Least Bell's Vireo, a federally endangered bird found only in wetland areas, could throw a monkey wrench in the County Flood Control District's plans to excavate the Hahamongna basin. Another federal endangered species, the burrowing owl, has also recently shown up. The Flood Control District's environmental documentation largely ignored recorded sightings of the federally listed endangered species as well as California species of special concern, namely the yellow warbler and the yellow-breasted chat. "These recent sightings should really focus the regulators on the importance of protecting critical habitat like Hahamongna and enforcing the Endangered Species Act," said Mitchell M. Tsai, attorney for the Arroyo Seco Foundation and Pasadena Audubon in the No Big Dig Lawsuit.

No Big Dig! Lawsuit Update

Attorneys Mitchell M. Tsai and Christina M. Caro filed the lawsuit against the Los Angeles County Flood Control District on December 11, 2014. After that, the hard work began, painstakingly going through the extensive administrative record and monitoring the regulatory permitting issues and process.


Here's the Skinny on the Hahamongna Sediment Lawsuit

The best way to find out about the issues and concerns involved in the lawsuit recently filed by the Arroyo Seco Foundation and the Pasadena Audubon Socity against LA County Flood Control District's sediment mining and trucking operation from behind Devil's Gate Dam in Hahamongna Watershed Park is to view the news conference held on December 20, 2014 to announce the lawsuit.

ASF's Tim Brick, Laura Garrett, Conservation Chair of PAS and attorney Mitchell Tsai are featured in the video explaining their concerns and the issues that will be contested in the No Big Dig lawsuit.

Lawsuit Campaign Soars Beyond Goal

Thank you to the 187 and counting Hahamongna supporters who have made our Indiegogo campaign, No Big Dig - the Lawsuit to Save Hahamongna, an overwhelming success. As of the February 5, 2015 deadline, we exceeded our goal by 34%, with a total of $33,566 raised. You made this happen!

The Indiegogo campaign funds will help cover our legal expenses as the Arroyo Seco Foundation and Pasadena Audubon Society take on the County's horrendous plan for Hahamongna and our neighborhoods. Click here to receive email updates on the lawsuit and other Hahamongna issues.

ASF, Pasadena Audubon Challenge The Big Dig!

The Arroyo Seco Foundation and Pasadena Audubon have stepped forward to take on LA County Flood Control District's Big Dig program for Hahamongna Watershed Park.

Lawsuit Announced  Support the Lawsuit

The Trucks Are Coming! 50,000 a Year!

Star News: See You In Court!

Supervisors Approve Devasting Plan
to Destroy Hahamongna Habitat

Plus: Dust, Noise, Air Pollution, Traffic Jams, Trails Closed!

What's Wrong with The Big Dig.

County Releases Massive Mining & Trucking Plan for Hahamongna

LA County Flood Control District has released their final environmental impact report on the sediment removal program for Devil's Gate Dam in Hahamongna Watershed Park. It's an old-style mining and trucking operation with devastating impacts on the nature and character of Hahamongna Watershed Park and on the surrounding communities.

Flood Control Releases Final EIR

LA County Flood Control District released the final Environmental Impact Report for the Devil's Gate Sediment Management Program in Hahamongna Watershed Park on October 20 and then rushed the program to the Los Angeles County Supervisors for their review and approval on November 12. Bucking overwhelming opposition, the Flood Control District held a series of three pro-forma public meetings to allow the public to comment on the Flood Control District's plan, but that was hardly enough time and opportunity to comment intelligently on a massive 7,864 page document.

To say the final EIR is a disappointment would be a historic understatment. As predicted, the Flood Control District selected one of their previous "alternatives," making only minor concessions to Pasadena and the 250 commenters who raised concerns about the $70-100 million sediment trucking program.

Pasadena Council Adopts Sediment Recommendations

On Monday, May 12, the Pasadena City Council unaminously adopted the recommendations of the Devil's Gate Sediment Working Group. This group was established by Pasadena to develop a more sustainable alternative to those presented in the LA County Flood Control District's Draft Environmental Impact Report on the Devil's Gate Sediment Removal and Management Project.

The Sediment Working Group's recommendations, if adopted, would substantially reduce the scope and negative impacts of the Flood Control District's program, while protecting the neighborhoods and rare environmental values of Hahamongna Watershed Park and the Arroyo Seco.

Recommendations of the Sediment Working Group

Council Agenda Report

Sediment Working Group Slides

SGV Tribune Endorses Pasadena Plan

The DEIR Comments Are All In

See What People Had to Say

The Trucks are Coming!!!

150,000 double-bed, diesel belching monsters, clogging streets, creating noise, dust, pollution, destroying precious habitat and severely impacting our neighborhoods

County Unveils $100 Million Plan to Destroy Region's Most Valuable Habitat

Find Out What You Can Do  Key Meetings Coming Up

The Sustainable Plan for Hahamongna

Dessi Says: "Save the Habitat of Hahamongna!"

My name is Dessi Sieburth and I am 11 years old. I have been with Pasadena Audubon Society for 3 years. I like to watch birds especially in the Hahamagna watershed, and I have seen over 60 species of birds in Hahamagna. I am here to speak against the sediment removal project of LA county. If we remove the sediment the bird's habitat will be destroyed. An endangered species, the Bells Vireo was seen and might be nesting in Hahamagna. I saw rare birds at Hahamanga such as Indigo Bunting, Lewis's Woodpecker, and Vesper Sparrow. If we destroy the habitat these birds will not come back. Please save the Habitat of Hahamagna!

(signed) Dessi Sieburth

County Releases Horrendous Plan for Hahamongna

Get the facts on the County plan on this website and on this factsheet: Fact Sheet

Here is the County's news release on the Devil's Gate Sediment Removal and Management Plan: Official Notice

Pasadena Officials Move Soccer Field to Muir

Pasadena officials have now eliminated plans for an additional soccer field at Hahamongna Watershed Park and to instead dramatically upgrade a rundown softball field at nearby Muir High Schoolin Northwest Pasadena. This is a win/win for everyone involved, expanding recreational opportunity while protecting Hahamongna, and another victory for Hahamongna activists and organizations to preserve our region's most valuable natural area.

Conceptual Design Released for Arroyo Seco Canyon Project

The Final Conceptual Design Report for the Arroyo Seco Canyon Project is now available for public review! Thanks to all those who participated in the workshops and sent in comments. ASF, the City of Pasadena, and Carollo Engineers worked hard to incorporate public input as much as possible. The result, we hope, is a project that will not only integrate water resources, habitat, and recreation but will also satisfy the needs and desires of the community.

Please feel free to direct any questions, comments, or concerns to Jonathan Frame (jonathan@arroyoseco.org) and Gary Takara (gtakara@cityofpasadena.net).

Click on the Image

Arroyo Moonrise (in Hahamongna Park) Original 18 x 24 oil painting © 2012 Karen Winters. KarenWinters.com

EIR In Preparation

LA County Flood Control District is now considering what alternatives there are for their massive sediment removal and management program at Hahamongna. County staff expects to release a draft of their environmental impact report next Fall. We will keep you informed of developments, so check back here regularly or sign up for updates.

Hahamongna Updates

Threats to Hahamongna

It's the most precious enviromental zone in our region, but it's under attack again.

A massive sediment and habitat removal program of the County of Los Angeles threatens to strip the basin of its rare riparian and alluvial scrub habitat


There's going to be a lot of action this year. We urge you to become informed about the issues and to get active to save this environmental treasure.

This site will keep you up to date on the latest developments in the campaign to preserve the natural richness of the area.