A Trip Down the Arroyo Seco – A Microcosm of Infrastructure, Nature, and Society Part I

– By Tonatiuh Rodriguez- Nikl



The Arroyo Seco (Dry Stream in Spanish) meanders down the San Gabriel mountains, into Pasadena, and later joins the Los Angeles River near Downtown. Over the course of two blog posts, we’ll take a trip down a roughly 20 km segment of the Arroyo, to see what it teaches us about nature, society, and infrastructure. This first part focuses on the relationship between nature and infrastructure. 

As we travel down the Arroyo we’ll observe how the natural stream is gradually slowed by dams, removed for groundwater, and contained in concrete channels. Yes, this infrastructure responds to important and legitimate needs for drinking water and flood control. At the same time, it damages the natural habitat, it is ugly, and it leads us to forget our dependence on the natural world. At the end of this post I’ll reflect briefly on social attitudes that led us to desire and build such infrastructure as well as a possible alternative.

I made this trip on a mountain bike, starting with an hour and a half climb into the San Gabriel Mountains. That wasn’t the most direct route, but it afforded me a great view from the ridge above the Arroyo. We’ll start our journey together from that ridge.

Entering Urban Space

We start the trip in the San Gabriel Mountains along the northern edge of the Los Angeles Basin. The Arroyo is visible in the canyon below, having originated about 5 km further up the mountain. We descend along switchbacks, overgrown in a few places with poison oak. Out here, there are few signs of human presence, but soon enough, the Arroyo arrives at its first dam. It’s hard to imagine that this gentle, trickling stream would ever need to be restrained by massive concrete dams, but the flood risk is real. After the dam, signs of development become increasingly obvious: segments of an abandoned road, check dams, and pedestrian bridges. A drinking fountain next to ranger houses is the first sign of potable water (some of it coming from the Arroyo). We then reach a paved service road that takes us out of the mountains and into the Hahamonga Watershed.

A view from the trail far above the Arroyo Seco. The streambed is seen in the bottom of the canyon.
The nearly dry riverbed meanders along the canyon. The highway and power lines remind us that we’re still near civilization.


The Arroyo Seco flows along a rocky streambed with trees on either side.
The Arroyo trickles by gently in the summer months.


Water flows over the top of a dam.
The Arroyo’s first dam. Built in the 1940s, the dam is filled with sediment and blocks fish passage.


The hiking trail crosses the Arroyo. The pile of tree trunks is a pedestrian bridge that was washed away by the heavy winter flow.


A drinking fountain with a house in the background behind a fence.
This drinking fountain outside the ranger complex is the first sign of potable water infrastructure.


Nondescript machinery behind a fence.
Pasadena water infrastructure near the Arroyo.


A check dam with boulders in the foreground.
A small check dam. There are others in the vicinity.


A weathered car rim sitting on dry boulders in the streambed
Along this part of the Arroyo, we see trash occasionally. One wonders how a rim ended up here.


Hahamonga Watershed Park

After its trip down the San Gabriel Mountains, the Arroyo Seco arrives at Hahamonga Watershed Park. The Park and surrounding areas, originally inhabited by the Tong-Va people, contain a frisbee golf course, trails, horse stables, developed picnic areas, and NASA’s Jet Propulsion Laboratory (JPL). At the south end of the park lies Devil’s Gate Dam, the main flood control structure along the Arroyo. Along the east bank of the Arroyo are spreading basins, which roughly speaking are large, flat holes into which some of the Arroyo’s water is pumped. Managing this watershed involves a constant tension between different priorities, including flood protection, groundwater management, and fish and habitat conservation. We’ll see two examples in the following paragraphs.

The first example involves an argument over the need for new spreading basins. The city of Pasadena draws much of its water from an aquifer that spans across the Hahamonga watershed. This aquifer’s water level has been declining steadily since 1910. To help recharge the groundwater and to obtain credits to use its water, the city diverts water from the Arroyo to the spreading basins. However, this damages the river habitat and, some people argue, is unnecessary because the groundwater could be recharged adequately by a naturally flowing stream. 

A second example starts in 2019 with a sediment removal project at Devil’s Gate Dam. Although the project entailed the removal of a large swath of riparian vegetation behind the dam and initially faced strong opposition from residents, local schools, and environmental activists, an effective public engagement process eventually gathered significant agreement, including support from the vocal  Arroyo Seco Foundation and the local native plant nursery that provided most of the plants for the restoration.

After playing its role in these contentious battles involving residents, environmental activists, and various government agencies, the Arroyo emerges from Devil’s Gate Dam to continue towards the Los Angeles River.

A bridge pylon painted with predicted flood depths.
The Arroyo crosses under a bridge. Note the red lines indicating the depths of the 10, 25, 50, and 100 year floods


Spreading basin water in the foreground and water flowing through pipes at the far end of the basin.
Water is pumped out of the Arroyo into a spreading basin.


A view of several dry spreading basins with the mountains in the background.
Few of the spreading basins are used regularly.


A screenshot of a map showing Pasadena's border, which includes a long, thin portion that contains the Arroyo.
Pasadena’s borders leave little doubt about the importance of water. Notice the long finger extending from northwest Pasadena to lay claim to the Arroyo.


A panoramic view of the dry streambed. Jet propulsion laboratory is visible on the right.
The main streambed. JPL is on the right and the spreading basins are on the opposite bank. Devil’s Gate Dam is on the left.


The dry streambed shows erosion caused by strong flow in the winter months.
After last year’s winter rains, the Arroyo was knee deep through here.


A view of the dam from the reservoir side. The water level is low.
The lake behind Devil’s Gate Dam is slowly starting to fill now that the sediment removal project is complete.


A view of the mountains, the reservoir, and the dam in the foreground.
We take one last look back at the mountains before we leave the dam behind and continue our journey down the Arroyo.


The Rose Bowl

After being harnessed by Devil’s Gate Dam, the Arroyo Seco discharges in a controlled flow, crosses under its first freeway and is soon confined to an uninviting concrete channel, one of many flood-control channels in the Los Angeles basin. (These channels may be ugly, but they make for good chase scenes!) The channel passes through the Rose Bowl area, which has several walking paths, playgrounds, and sport facilities. Along this stretch, the Arroyo meanders unceremoniously through a golf course (watered with potable water) and past the iconic Rose Bowl stadium. The Arroyo has transitioned from a central feature in the mountains to a hidden urban gutter.

A view from above the dam showing the water being discharged.
The Arroyo Seco exits Devil’s Gate Dam in a controlled flow.


A truck crossing on a freeway crossing a bridge. Graffiti is visible on the bridge.
Soon after exiting the dam, the Arroyo passes under its first freeway, Interstate 210.


A lushly vegetated segment of slow-flowing stream.
Less than 100 meters from here the Arroyo enters the concrete channel.


 A channel with diagonal walls and a flat bottom except for a slightly deeper section in the middle through which water flows.
The Arroyo meanders past a golf course. A project was considered to use non-potable water for irrigation but NIMBYism killed the project. The golf course is still irrigated with potable water.


A sign on a fence reading "Trespassing - Loitering Forbidden by Law".
The Arroyo is much less inviting along this stretch. It is no longer a public resource, but an infrastructure facility owned by the Department of Public Works.


A man on a bicycle riding in the channel.
This man was collecting lost golf balls.


The channel with the Rose Bowl stadium visible in the background.
The Arroyo passes by the iconic Rose Bowl stadium.



This journey down the Arroyo Seco points to a relationship between humans and nature based on control and certainty. The dams and the channels will undoubtedly stop the floods. The simple geometry of the concrete channel tames the natural stream and produces nice, predictable flow. Similarly, the spreading basins render it unnecessary to understand infiltration along the natural but complicated streambed. Control and certainty aren’t necessarily bad (after all, who would argue for impotence and uncertainty?) but they are bad if they are achieved at the cost of neglecting important considerations. This infrastructure is ugly, uninviting, damages the natural habitat, and invites us to deplete our water stores thoughtlessly while keeping lawns green in an arid climate; these and other similar considerations were ignored when the infrastructure was designed.

We like to think of our world in terms of “problems” that we can “solve” with technological artifacts. Coming from a problem-solution paradigm, the problem of insufficient water entering the aquifer is solved by building something to put more water in. The problem of floods is solved by building dams and channels to slow and control the water.  This approach is intellectually easy and politically attractive (“Look, I solved your problem. Reelect me!”) but the very act of defining a problem in a large, complicated system like the Arroyo, reduces the scope of the relevant issues considerably, spawning secondary problems in the wake of the so-called solutions. Infrastructure tends to lock in these secondary problems because it is durable and expensive to replace.

How about instead, we reframe these issues as maintenance challenges? Let’s ask how we can maintain the interconnected systems that sustain us. Let’s view ourselves and our relationship to the rest of the world – the Earth and all its inhabitants – not through a lens of control but one of continuous cycles of understanding, adaptation, and monitoring with a sensitivity to the many physical and social influences involved as well as the wide range of human needs that are served.

Coming Next

Check out “A Trip Down the Arroyo Seco: A Microcosm of the Relationship between Technology, Nature, and Society Part II”. Here will continue our trip down the Arroyo, turning our attention to socioeconomic observations. The stark contrast we observe between the affluent and poor residents along the Arroyo’s banks will lead us to reflect on the ways that socioeconomic factors led to the channelization of the Arroyo almost a century ago.

Preferred citation: Rodriguez- Nikl, Tonatiuh. (2022, June 13). A Trip Down the Arroyo Seco - A Microcosm of Infrastructure, Nature, and Society Part I. The Maintainers. https://themaintainers.org/arroyo-seco/