The Mount Wilson Toll Road is today a popular hiking trail in the San Gabriel Mountains above Pasadena, California. Nine miles long, about twelve feet wide, unpaved and littered with rocks from landslides, it hardly looks like a road at all, let alone one that was once critical to the operations of one of the most important astronomical observatories of the 20th century. Yet this trail was the only automobile route up Mount Wilson from 1907 to 1935, and the story of how it was built reveals a web of scientific ambition, racial hierarchy, environmental constraint, and invisible labor that shaped American astronomy in ways that are still worth reckoning with.

In an article published in Historical Studies in the Natural Sciences—and presented last year at AIP’s Early Career Conference—astrophysicist and historian Eun-Joo Ahn reconstructs the history of the trail-widening that made Mount Wilson Observatory possible, arguing that the road should itself be understood as scientific infrastructure. Far from a passive backdrop to the telescopes and domes at the summit, the road was an active force that determined what kind of science could be done, when it could be done, and who did the work to make it happen.

Pasadena wants an observatory

The origins of the Toll Road stretch back to the 1880s, when Southern California boosters—local businessmen and local leaders, including newspaper editors, bankers, and real estate agents—competed fiercely with Northern California for prestige and investment. The Lick Observatory on Mount Hamilton had brought national attention to the San Jose area, and Pasadena’s civic leaders wanted something comparable.

A wealthy banker named Edward F. Spence pledged funds for a telescope even larger than Lick’s, and Pasadenan businessmen formed a railway company to build access up the mountain. But Spence died without providing for the telescope in his will, the railway company reorganized into a toll road company, and the road they actually built was only two to four feet wide, passable by foot and pack animal, but nothing more. The mountain was simply too steep, too prone to landslides, and too expensive to carve into for the capital these entrepreneurs could muster.

When astrophysicist George Ellery Hale founded Mount Wilson Observatory in 1904 with Carnegie Institution of Washington funding, he initially assumed that local developers or railway magnate Henry Huntington would take care of building a proper road. They did not. Huntington’s surveyors estimated costs of $65,000 per mile, roughly $9.2 million in today’s currency, for the full route. A newly incorporated railroad company raised only $15,000 in subscriptions, barely enough to pay its surveyor. The energy that characterized Southern California’s boom years was not matched by the financial commitment needed to overcome the San Gabriels’ formidable geology.

Japanese laborers and the work of widening

By 1906, Hale could wait no longer. He needed the road widened to transport parts up the mountain for two large telescopes, the sixty-inch reflector and the sixty-foot solar telescope. Southern California’s rainy season, which triggered landslides from December through March, meant that all construction and transport had to happen during the dry months. A delay of even one season would cost a full year of observation time. Hale persuaded the Carnegie Institution to allocate $15,000 for the work and brought in Godfrey Sykes, an English-born engineer from the Carnegie-funded Desert Laboratory in Tucson, to oversee it.

Sykes and his brother Stanley, who served as foreman, initially sought European immigrant laborers, what they called “white labour,” but found only workers of the “migrant type” interested in the grueling task of chipping a road out of a mountainside with picks and shovels. They turned instead to Japanese immigrant laborers, recruited through employment offices in downtown Los Angeles or the Little Tokyo district.

As Ahn details, the hiring was shaped by intersecting forces of racial prejudice, labor economics, and anti-union sentiment. Japanese immigrants occupied a precarious position in early 20th-century California. The Chinese Exclusion Act of 1882 had curtailed Chinese immigration, and Japanese workers partially filled the resulting labor gap, only to face similar hostility from white Americans who grouped all Asian immigrants together as racially and culturally inferior. The American Federation of Labor barred Japanese workers from its affiliates in 1906. Hale, who had been burned by union strikes at the San Francisco iron works making his telescope parts, valued precisely this vulnerability: Japanese day laborers, hired without contracts, could be paid lower wages and dismissed at will.

The workers were organized into racially segregated teams. Two Japanese crews, “Kai’s gang” working upward from the base and “Joe’s gang” (later “Honda’s gang”) working downward from the summit, used picks and shovels to chip away at ancient rock on slopes so steep that animals and machinery were useless. A separate “mule gang” of white laborers followed behind with mules, plows, and scrapers to grade the cleared sections.

Disaster on the mountain

Progress was rapid through the summer and fall, but the rainy season arrived weeks earlier than expected. Starting in late November 1906, a series of storms triggered rockslides that buried completed sections of road, collapsed the burlap-sack retaining walls that Sykes had improvised to save money, and made access to the work site impossible for days at a time. A worker named Kakichi Matsushita was killed on December 12 when rain-softened ground collapsed beneath him as he tried to dislodge a rock. An inquest ruled the death accidental, and the observatory faced no legal liability.

Ahn’s close reading of the correspondence between Hale and Carnegie president Robert Woodward following Matsushita’s death is particularly revealing. Neither man referred to the deceased worker by name, only as “the Japanese laborer.” Woodward praised Hale for paying funeral costs as a “graceful duty” and expressed relief that the death could not be attributed to observatory negligence. As Ahn observes, Japanese workers were essentially invisible to their employers, becoming noticeable only when their circumstances threatened unwanted publicity or financial liability.

Work halted for the winter. A single unnamed Japanese worker was retained to watch the retaining walls through the storms, a man Hale called “very faithful and efficient” yet still did not name in his reports. When spring came, a local stonemason named George D. Jones took over supervision from Sykes, whose unfamiliarity with the local climate and geology had contributed to cost overruns that nearly doubled the original budget. About eighty Japanese workers completed the remaining mile of road, and by late May 1907 the first automobile made its way up the mountain.

What the road reveals

Ahn’s article makes a case that resonates well beyond Mount Wilson. By framing the road as scientific infrastructure, she shows how the natural environment actively shaped the observatory’s scientific program. The steepness of the San Gabriels, the instability of billion-year-old rock on a geologically young and still-rising mountain range, the seasonal rhythm of rain and drought: all of these constrained what astronomers could achieve and when. The road determined which telescopes could be installed, how quickly the observatory could expand, and when observations could begin.

The road also made visible the social hierarchies embedded in scientific work. The Japanese laborers who carved the road occupied an intermediate position: essential to the project, yet excluded from the community it served, and eventually erased from its history, even as photographs of their work remained in the observatory’s archives.

This pattern of scientific institutions built on contested land through invisible labor is not unique to Mount Wilson. Ahn draws comparisons to the contemporaneous construction of the Lick Observatory road using underpaid Chinese laborers three decades earlier, and to the ongoing controversies at Mauna Kea in Hawai’i, where the proposed Thirty Meter Telescope has catalyzed profound debates about indigenous sovereignty, environmental stewardship, and the assumptions astronomers make about which mountains are “available” for science.

At Mount Wilson, those debates never happened, not because the issues were absent, but because the erasure of prior claims was already so complete that the transformation of the mountaintop felt, to its white American beneficiaries, like the natural order of things.

The Toll Road fell out of use in 1935 when the Angeles Crest Highway provided a new route to the summit. Its owners turned it over to the US Forest Service. As Ahn points out, today’s hikers, navigating its hairpin turns with views stretching to the Pacific, encounter no sign that the trail beneath their feet once carried telescope parts, that Japanese immigrants broke its rocks by hand, or that a man named Kakichi Matsushita died there in the service of American astronomy. Ahn’s work ensures that, at least in the scholarly record, these facts are no longer invisible.

Rebecca Charbonneau
American Institute of Physics
rcharbonneau@aip.org

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