The ARC

As the Arroyo Seco stream descends from the San Gabriel Mountains, it travels about six miles south through La Cañada Flintridge, Altadena, and Pasadena until it reaches San Rafael Creek near the border with South Pasadena. When the stream reaches the area where the three cities -- Pasadena, South Pasadena, and Los Angeles -- meet, the stream and channel veer to the west in a graceful curve through an area that has great potential for naturalization, stream restoration, and flood protection, the Arroyo ARC.

The Arroyo ARC is a three-mile stretch of the Arroyo watershed that begins at the San Rafael Bridge in Pasadena and includes South Pasadena and parts of Los Angeles, stretching down to the York Boulevard Bridge including the stream and surrounding canyon. It is an important transition zone as the Arroyo Seco stream flows from the San Gabriel Mountains to the Los Angeles River.

The dotted line represents the city boundaries with Pasadena (P) in the upper region, Los Angeles (LA) to the left, and South Pasadena (SP) to the right.

San Rafael Bridge

San Rafael Bridge is a picturesque bridge that crosses the Arroyo about three hundred yards above the South Pasadena boundary. There is a ragged stone staircase from the San Pascual Avenue on the east side to the bottom of the Arroyo canyon where a small pedestrian bridge crosses the flood channel. San Rafael Bridge was built in 1922, before the stream was channelized after World War II. That means there is real potential for stream restoration in this area.

San Rafael Creek

San Rafael Creek is a small stream that begins in the Annandale Canyon area near Eagle Rock and travels south between western Pasadena and northeast Los Angeles to the private Johnston Lake off Laguna Road. It is a largely natural stream that is not lined for most of its course. At Johnston Lake the stream moves east through a series of backyards until it reaches the confluence with the Arroyo Seco stream. As it descends down the slope from Laguna Road to the confluence with Arroyo Seco, the creek is channelized for only 250 feet of concrete. At the bottom is a 5-acre site that is not accessible to the public but would be an ideal site for wetlands and a natural transition to the Arroyo Seco stream.

San Pascual

The San Pascual Site begins with a massive equestrian facility, San Pascual Stables, that has been a major source of contamination of the Arroyo Stream for many years. The stream is bounded on both sides by municipal parks, on the west by the City of Los Angeles San Pascual Park and on the east by South Pasadena’s Arroyo Park. The San Pascual neighorhood lies to west. The historic Garfias Stream is hidden in a culvert underneath the South Pasadena park as it flows into the Arroyo Seco stream near San Pascual Avenue. The San Pascual site also includes San Pascual Park, a Los Angeles park that straddles the Arroyo Seco stream.

The Flood Channel

The flood channel, one of the main features of the ARC, robs the area of its natural vitality. Unlike the smooth concrete walls that line most of LA County’s flood channel in the Arroyo, the channel in South Pasadena is largely made up of grouted arroyo stones that were used during the construction of the channel in the 1930s at the insistence of South Pasadena officials who wanted a more “natural” channel. While the intent was admirable, the result is a poor-quality, deteriorated channel through the most vulnerable stretch of the Arroyo Seco, right underneath and alongside the Arroyo Seco Parkway (Pasadena Freeway).

The Island

South of the freeway, the channel passes alongside the tennis courts and the South Pasadena Golf Course. This is also the area where the bicycle path begins and continues to the York Boulevard Bridge. Across the channel is a large island wasteland that flanks the freeway. This is an ideal spot for naturalization and broadening the floodplain for enhanced protection.

The South Pasadena Nature Park

The Nature Park, aka the South Pasadena Woodland and Wildlife Park, is a wonderful grassroots restoration project at the southern tip of South Pasadena next to flood channel. In the last twenty years local residents have created and sustained a wonderland of native plants and habitat of the sort that once characterized most of the Arroyo Seco.

The York Boulevard Bridge

This bridge marks the southern limit of the Arroyo ARC and the dividing line between the cities of South Pasadena and Los Angeles.

Flood Protection

The Arroyo Seco hasn’t had a massive flood for many years (1969), but that doesn’t mean it won’t in the climate-warped future. The devastating flood of 1914 in the Arroyo Seco led to the founding of the Los Angeles County Flood Control District and to its first dam five miles north of the ARC at Devil’s Gate in Pasadena. Climate scientists predict that the future will feature occasional but erratic massive floods and extended dry conditions that can be mitigated by nature-based solutions.

A little-known 2011 study prepared for the LA County Flood Control District found that the Arroyo Seco flood channel is not equipped for the type of floods that will likely occur in the future. It predicts that as many as 650 homes in the Highland Park area could be damaged by future floods.

Steelhead in the Arroyo

Before the construction of Devil’s Gate Dam in the Arroyo Seco in 1920, this stream was arguably the key stream in the Los Angeles River Watershed for the Southern California steelhead (Oncorhynchus mykiss), now an endangered species. The steelhead are genetically the same as the rainbow trout in the mountain watershed of the Arroyo Seco. In June of 2024, the California Department of Fish and Wildlife documented that there were more than 4,000 rainbow trout wannabe steelhead in the Arroyo Seco mountain stream. To bring back the steelhead to the Arroyo Seco and the Los Angeles River, there needs to be a series of refuges for the fish along the Arroyo as they make their journey north or south. The Arroyo ARC represents a key opportunity for such refuges in a vital transition zone.

Goal

The restoration of the Arroyo Arc will be a complete transformation of the area to restore the natural character of the Arroyo Arc, to provide enhanced conditions for fish and wildlife, and to improve flood protection for nearby neighborhoods including San Pascual and Garvanza.

We propose that the restoration of the Arroyo Arc should be a major component of the Arroyo Seco Ecosystem Restoration Program that LA County and other local agencies and stakeholders are now developing.