Hahamongna Updates

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.

County Proceeds with Emergency Measures at Devil's Gate

September 9, 2011 - The County of Los Angeles has completed the sediment storage portion of their emergency program at Devil's Gate Dam in Hahamongna. In this phase, County Department of Public Works work crews and contractors removed 13,000 cubic yards of sand and sediment from the area immediately north of the dam and moved it to the former Johnson Field site on the east side of the flood basin.

The crews are now working on other steps to improve access to the valves and spillway outlets on the dam to prevent blockage in the event of floods.

The County's emergency program, which will continue through October, is completing measures designed to reduce the flood threat while an Environmental Impact Report is being compiled for the much larger effort the County is now planning. The initial sediment storage program is less than 1% of the amount that the County intends to remove from the Hahamongna basin.

Sediment removal

Immediately above the dam a dozer is loading a truck to move up to 25,000 cubic yards away from the dam valves.

Sediment removal 3

Looking from Devil's Gate Dam, the truck is moving the sediment to a temporary drying mound.

Sediment removal

This is the scene from the east side of Devil's Gate Dam looking northwest. The dozer is compacting the sediment into a mound for drying. Most of the material will then be moved to the former Johnson Field for temporary storage, while organic material such as tree branches will be trucked out of the basin.

photo credit: Don Bremner

Threats to Hahamongna

It's the most precious enviromental zone in our region, but it's under attack again. There's no question about it: 2011 will be a year of decision for Hahamongna.

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


Pasadena is forging ahead with an ill-conceived plan to add a parking lot and a soccer field to the center of the basin.


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.