The park's name translates to 'fruit of the valley' in the Tongva language.
The Devil's Gate Dam, located within the park, was constructed in 1920 as the first flood control dam in Los Angeles County.
It is a designated stop on the 28-mile Arroyo Seco greenway path.
The park contains one of the oldest and most established disc golf courses in Southern California.
It sits at the precise geological junction where the San Gabriel Mountains meet the San Rafael Hills.
The basin serves as a groundwater recharge facility for the Raymond Basin aquifer.
The area is home to the last remaining stand of native Southern California sycamore trees in the Arroyo Seco.
Hahamongna Watershed Park serves as a 300-acre basin for the Arroyo Seco, designed for flood control, water conservation, and ecosystem restoration at the base of the San Gabriel Mountains. The name originates from the Hahamogna tribe of the Tongva people who historically inhabited the area. The park features an extensive network of multi-use trails connecting to the Gabrielino National Recreation Trail, leading into the Angeles National Forest. It functions as a capture basin for the Devil's Gate Dam, a key piece of infrastructure in the region's flood management system. The landscape transition between mountain canyon and alluvial plain supports significant riparian habitats. Visitors find equestrian rings, disc golf courses, and picnic facilities integrated into the wildland-urban interface. Ongoing sediment removal projects periodically impact accessibility to specific trail sections within the basin floor. The site remains a critical node for migratory birds and local wildlife movement between the mountains and the Los Angeles basin.
The elevated overlook near the dam parking area providing a panoramic view of the basin and mountains.
Bring a printed trail map, as mobile service is unreliable in the deeper canyon sections.
Wear sturdy, closed-toe hiking footwear to navigate loose gravel and uneven terrain on the basin floor.
Keep a safe distance from active sediment removal machinery if construction is ongoing.
Do not attempt to walk on the basin floor during or immediately after heavy rain due to flood risks.
Trail access may be restricted during periods of high water release or active sediment removal operations.
Stay on marked trails to protect sensitive riparian habitats; keep dogs on a leash at all times.
