The Arroyo de la Sacatela ran through Bimini Slough, shown here in an undated photo. The city filled in the slough in the 1930s , and the Arroyo de la Sacatela is today a series of storm drains. Courtesy of the Los Angeles Area Chamber of Commerce Collection, USC Libraries.

As any hike through the mountains will confirm, different geographies govern wild and urban areas. In the wild, peaks, ridges, and watercourses help us navigate, and as we move through the landscape it's difficult to miss how geologic uplift and erosion have shaped the land. But in the city, a different set of features makes a landscape navigable. The freeways, light rail lines, and the boundaries between neighborhoods tell us where we are. Natural processes are at work in the city as they are in the wild, but the built environment renders them invisible. We see mountains on the horizon, but we risk forgetting entire hills that once rose in the center of the city.

In recent years, Los Angeles has worked to rediscover elements of its lost, wild geography. Activists have transformed the long-neglected Los Angeles River -- once dismissed as a storm channel -- into a 50-mile-long symbol of the promises and frustrations of Southern California environmentalism. In western Los Angeles, scientists, geographers, and other researchers have mapped in precise detail the locations of vernal pools, marshes, meadows, and other wetlands that once dotted the Ballona Creek watershed.

Archives have played a key role in rediscovering another forgotten feature of L.A.'s wild geography: the extensive system of creeks, arroyos, and other watercourses that once flowed through present-day Los Angeles. Fed by springs issuing from vast underground aquifers, storm runoff, or some combination of the two, these streams once crisscrossed the entire city. Today, many of them have suffered a similar fate as the Los Angeles River: paved over, buried and converted into storm drains, or eliminated altogether. Most Angelenos walk or drive over them every day without realizing it.

Not Jessica Hall. Since 2008, the landscape architect has traced the former routes of L.A.'s waterways on the L.A. Creek Freak blog, which she founded with artist and L.A. River activist Joe Linton. By studying the maps, photographs, and other documents preserved in the region's archives, Hall has reconstructed a surprisingly wet L.A. landscape, braided with dozens of streams that now lie buried beneath streets and parking lots.

East of the Los Angeles River, the Arroyo de las Pasas once originated in the hills of Montecito Heights and flowed southwesterly toward its confluence with the Los Angeles River. Today, much of the arroyo is a series of culverts underneath Lincoln Park and the USC Health Sciences Campus.

West of downtown Los Angeles, the Arroyo de Sacatela flowed south through present-day Los Feliz and Koreatown on its way to the inland cienega of the Ballona Creek watershed. In 2008, the Militant Angeleno discovered remnants of the arroyo while retracing the watercourse's path.

Even the concrete-and-glass landscape of downtown L.A. was once home to a willow-lined creek; the Arroyo de los Reyes originated north of present-day Echo Park, flowed through a ravine, and emerged just south of Bunker Hill near what is today Pershing Square. Upstream, a private water company dammed the arroyo's canyon in 1868 to create a reservoir, which we know today as Echo Park Lake.

Maps have proven to be some of Hall's best historical evidence. Old irrigation maps and USGS topographical surveys often show intermittent streams flowing through what are today parking lots and real estate developments. In Sacramento, Hall perused Henry Hancock's landmark 1858 survey of Los Angeles in the California State Archives and rediscovered the names of three lost streams.

Even where streams are unmarked on topographical maps, soil maps -- produced initially for agricultural purposes -- provide clues in their records of soil composition as to where watercourses may have flowed.

Hall has also used photographs to locate streams. Riparian ecosystems often stand out in aerial photographs at such institutions as the Pasadena Public Library, UCLA Department of Geography, and Whittier College. Even photos taken at ground level may hint at a stream's existence; images of flooded streets after a heavy rain may indicate that a road follows the former path of an arroyo.

In some cases, the built environment itself preserves evidence of the city's lost streams. In 1906, the city built a bridge to carry Macy Street (now Cesar Chavez Avenue) over Arroyo de las Pasas. Today, the bridge remains, but the arroyo has been filled in, replaced with train tracks and the concrete lanes of the San Bernardino (I-10) Freeway.

Los Feliz's Shakespeare Bridge, likewise, carries Franklin Avenue over the now-defunct Arroyo de la Sacatela, as the Militant Angeleno documented. Downstream, another bridge transports Sunset Boulevard over the former path of the arroyo, now occupied by Myra Avenue.

Google Earth satellite imagery of Los Angeles overlaid with L.A.'s historical streams and wetlands. Courtesy of Jessica Hall, L.A. Creek Freak.

This detail of an 1897 USGS map records the paths of several streams on L.A.'s Eastside, including the Arroyo de las Pasas . Courtesy of the Henry J. Bruman Map Collection, University of California, Los Angeles Library.

The same map records the path of several streams west of downtown L.A., including the Arroyo de la Sacatela and the Arroyo de las Reyes. Courtesy of the Henry J. Bruman Map Collection, University of California, Los Angeles Library.

Detail of a 1916 soil survey of the Los Angeles area by the U.S. Department of Agriculture, Bureau of Soil. Courtesy of the Map Collection, Los Angeles Public Library.

After years of digging through the archives and then confirming her findings with field visits, Hall is now an experienced stream detective.

"I know how to read the topography," she explained. "I can look at a landform and guess what I'm seeing."

A 2006 L.A. Weekly profile followed Hall as she scaled chain-link fences and waded through stagnant waters in search of hidden streams. But archival evidence is still an essential part of her research.

"Guessing is one thing, but actually having the document that demonstrates where something was is much more convincing and powerful."

And Hall has had a lot of convincing to do. When she began looking for signs of abundant water in L.A.'s historical ecology -- not just in streams but also in in springs and wetlands -- she ran into the persistent misconception that the city's natural state is desert.

"There were people who laughed at me behind my back," she said.

Scholarly investigations into historical wetlands and the extensive educational efforts centered on the L.A. River have softened such misunderstanding of the landscape, but the city's lost streams are a particularly salient example of L.A.'s wild geography. Often the streams flow directly through neighborhoods and through backyards, reinforcing the idea that we live not just in cities and blue-sign districts but also watersheds.

By reminding Angelenos of the city's natural features, the dead or buried streams evoke an image of an urban ecosystem where issues like environmental justice, ocean water quality, and flood hazards are interconnected.

Hall hopes that, by promoting greater understanding of such concerns, the rediscovered streams will drive residents to action.

"I would hope they would start advocating with their local governments to restore these small streams," Hall said.

Storm drains through schoolyards and city parks provide a place where communities might muster the necessary political will and practical means to "daylight" (to use Hall's term) the buried waterways.

"Because they are small streams, we have an opportunity to understand on a technical level how they function without creating a hazard to life and property."

1929 aerial view of the Arroyo de la Sacatela at Third Street and Vermont Avenue.

Circa 1887 view of Second Street Park, which was home to a lakelet just south of Echo Park. The park was located in the canyon of the Arroyo de los Reyes. Courtesy of the Title Insurance and Trust / C.C. Pierce Photography Collection, USC Libraries.

1943 view of the Macy Street viaduct over the Arroyo de las Pasas ' former route. Today, the bridge carries Cesar Chavez Avenue over the Interstate 10 freeway.

In this circa 1922 photo, the resurgent Arroyo de la Sacatela floods the intersection of Sixth Street and Mariposa Avenue. Courtesy of the Security Pacific National Bank Collection, Los Angeles Public Library.

Correction, Sept. 7: In an earlier version of this post, a photo caption incorrectly stated that Second Street Park later became Echo Park. In fact, as reader Scott Fajack notes, Second Street Park was located downstream along the Arroyo de los Reyes from Echo Park, near the present-day intersection of Glendale Boulevard and First Street.

Many of the archives who contributed the above images are members of L.A. as Subject, an association of more than 230 libraries, museums, official archives, personal collections, and other institutions. Hosted by the USC Libraries, L.A. as Subject is dedicated to preserving and telling the sometimes-hidden stories and histories of the Los Angeles region. Our posts here provide a view into the archives of individuals and cultural institutions whose collections inform the great narrative—in all its complex facets—of Southern California.

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