Save Hahamongna Watershed! It's still a BIG DIG, and we still say NO!

Save Hahamongna Watershed! It's still a BIG DIG, and we still say NO!

July 4, 2018
Petition to
Supervisor Members of the LA County Board of Supervisors and
Signatures: 6,051Next Goal: 7,500
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Why this petition matters

Supervisor Kathryn Barger and the LA County Board of Supervisors,

We thought we had won a victory to protect Hahamongna and lessen the impacts of the sediment removal project November of 2017 when your Board voted to substantially modify and reduce the Flood Control District's Big Dig program for Hahamongna Watershed / Devil's Gate Dam Sediment Removal Project, agreeing to decrease by 30% the amount of soil and habitat to be excavated and trucked away from behind Devil’s Gate Dam.  But LA County Public Works is defying this agreement and pushing forward with their original plan to dig up and remove 70 acres of habitat, with work set to begin in November of this year. Excavating 70 acres will turn our watershed with its rare riparian habitat into a crater, devoid of life. The community strongly opposes what is still the BIG DIG! 

Hahamongna Watershed in the Arroyo Seco is the key connecting corridor linking the San Gabriel Mountains to Downtown Los Angeles, providing water, sediment, habitat and wildlife to the entire LA River system through the Arroyo Seco. Its rich riparian resources are too valuable to be turned into a maintenance area for the Flood Control District.

We implore the County Supervisors to enforce the agreement made last November by working with the community to develop a slow, steady sediment removal plan that reduces the amount of acreage to be excavated and the other negative impacts by 30%. The plan should be resilient, informed by science and work to: re-establish the natural systems that make the Arroyo Seco one of the key tributaries to the LA River. It should protect the wildlife corridor and habitat for endangered species, such as the Least Bell’s Vireo, and save the trees that absorb CO2, diminishing the greenhouse effect and improving air quality.

A slow, steady sediment removal plan would also reduce the impact of noise, dust, and traffic and air pollution on surrounding communities and provide flood protection that works with nature instead of against it. 

Please work with us to Save Hahamongna for future generations. 

Save the Arroyo Seco Hahamongna Watershed

It’s Still a Big Dig! And We Still Say NO!


Stay up to date at:


The US Army Corps of Engineers has issued a public notice regarding their permit for the Devil's Gate Sediment Mining and Trucking program, aka the Big Dig. They invite all those who are concerned about Hahamongna to make comments regarding the project and the USACE's responsability to protect the environment.


The Hahamongna Watershed is a 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 the Hahamongna Watershed go the way of other lost environmental treasures in Southern California.

The Meaning of Hahamongna:
The word means "Flowing Waters, Fruitful Valley" in the native Tongva language.

Threats to Hahamongna
It's the most precious environmental zone in our region, but it's under attack again. A massive sediment and habitat removal program of the County of Los Angeles will strip the basin of its rare riparian and alluvial scrub habitat and a vital corridor for wildlife.

What's wrong with the Big Dig: CLICK HERE

The Sustainable Plan for Hahamongna: CLICK HERE

Riparian Habitat
Much of Hahamongna Watershed consists of a riparian zone, a region of direct interaction between terrestrial and stream systems. This zone directly influences the Arroyo Seco stream channel and eco-system.

The riparian wetlands, which occur on the edge of the steam, feature woody vegetation such as white alder, cottonwood, and willow. Riparian habitats are characterized by lush vegetation and a rich diversity of species. Elderberries, wild rose, and blackberries grow beneath willow, oak, laurel, sycamore and cottonwood trees. Songbirds, woodpeckers, hawks, owls, frogs, snakes, skunks, raccoon, coyote and deer thrive here. The healthy riparian corridor through Hahamongna once was critical habitat for salmon, steelhead trout and other anadromous fish. Today trout still swim in the mountains just north of Hahamongna.

Freshwater Marsh Habitat
In the southern part of the Hahamongna basin, flow from Flint Canyon and the western portion of the Arroyo Seco watershed has established a lovely pond or freshwater marsh. Freshwater marsh habitat grows in and near ponds, low lying areas that accumulate runoff and slow-moving segments of streams. This pond is vegetated mostly with herbaceous plants, predominantly cattails, sedges, and rushes. Freshwater marshes have mineral soils that are less fertile than those of salt marshes but exhibit a greater variety of plant species.

Alluvial Scrub Habitat
Hahamongna is a canyon and flood basin consisting of the silt, sand, gravel, rocks and similar material deposited by the Arroyo Seco stream as it descends from the mountains. These alluvial canyons are particularly rare in Southern California. Most have been severely degraded by development and other human activity.

The Hahamongna Watershed is a particularly good example of alluvial fan sage scrub habitat, a Mediterranean shrubland type that occurs in washes and on gently sloping alluvial fans. Alluvial scrub is made up predominantly of drought-deciduous soft-leaved shrubs, but with significant cover of larger perennial species generally found in chaparral. Alluvial scrub typically is composed of scale broom, white sage, redberry, California buckwheat, Spanish bayonet, California croton, cholla, tarragon, yerba santa, mule fat, and mountain-mahogany.

Riversidean Alluvial Fan Sage Scrub, such as that found at Hahamongna, is the most threatened of Coastal Sage Scrub associations with less than 15,000-acres remaining worldwide ... making it more endangered than ancient redwood forests of the Pacific Northwest and tropical rainforests.

California Chaparral
The slopes of Hahamongna are crowded with chaparral, a shrubland or heathland plant community found primarily in California and in the northern portion of the Baja California peninsula, Mexico. It is shaped by a Mediterranean climate (mild, wet winters and hot dry summers) and wildfire. Similar plant communities are found in the four other Mediterranean climate regions around the world, including the Mediterranean Basin (where it is known as maquis), central Chile (where it is called matorral), South African Cape Region (known there as fynbos), and in Western and Southern Australia.

A typical chaparral plant community consists of densely-growing evergreen scrub oaks and other drought-resistant shrubs. It often grows so densely that it is all but impenetrable to large animals and humans. This, and its generally arid condition, makes it notoriously prone to wildfires. Although many chaparral plant species require some fire cue (heat, smoke, or charred wood) for germination, chaparral plants are not "adapted" to fire per se. Rather, these species are adapted to particular fire regimes involving season, frequency, intensity and severity of the burn.

Oak Woodland
California oak woodland is a plant community found throughout the California chaparral and woodlands ecoregion of California and northwestern Baja California. Oak woodland is widespread at lower elevations in coastal California, interior valleys of the Coast Ranges, and in a ring around the California Central Valley grasslands. The dominant trees are oaks, interspersed with other broadleaf and coniferous trees, with an understory of grasses, herbs, geophytes, and shrubs. Oak savannas occur where the oaks are more widely spaced.

The Oak woodlands of Southern California and coastal Northern California are dominated by Coast Live Oak (Quercus agrifolia), but also include Valley Oak (Q. lobata), California Black Oak (Q. kelloggii), Canyon live oak (Q. chrysolepis), and other California oaks. Hahamongna also includes Englemann oaks, a distinctive cousin of the Blue Oak that was called the Pasadena Oak by the early settlers of our region.

The Hahamongna to Tujunga Wildlife Corridor Initiative of the Arroyos & Foothills Conservancy and has a goal of linking the San Gabriel Mountains at Hahamongna Watershed Park to the San Gabriels at Big Tujunga Wash for wildlife passage through the San Rafael Hills and the Verdugo Mountains, a 20-mile long Corridor. A successful project will bring to life 2,400 acres of habitat in the San Rafaels and 11,000 acres in the Verdugos by connecting them with the 700,000-acre Angeles National Forest in the San Gabriels. Wildlife can then live in these urban hills with ready access to others of their species in the abundant range of the San Gabriels, assuring genetic diversity.

Support now
Signatures: 6,051Next Goal: 7,500
Support now