Tales from the tunnels, the railroad and the Cuesta Grade

Posted by David Middlecamp on October 3, 2013 

SOON TO CLOSE...Because of maintenance cost, this long railroad tunnel on Cuesta grade will soon be plugged. Southern Pacific company is building around the nearly 900-foot tunnel No. 10 on Cuesta grade. (Telegram-Tribune photo) published Jan. 11, 1962


It has been there all our lives.

Most take it for granted, the railroad hugging the west side of Cuesta Grade, snaking just below the ridge top.

It was an engineering marvel of its day.

There was no guarantee that the Southern Pacific line would come to San Luis Obispo.

Facing heavy construction costs, the railroad demanded that local board of trade provide the right of way for the railroad and space for a depot, workshops and warehouse. 

One survey had mapped a route that exited the Santa Lucia Range via the Corral de Piedra creek, another through Morro Bay.

It was a case of Southern Pacific saying, "Give us the deed before we build."

In 1893, San Luis Obispo roads were poor, and the best route to San Francisco was via steamer. The railroad was seen as an economic boon, and for many years it would be the largest employer in town.

The city fathers organized a committee of bankers, land investors and businessmen, including Tribune editor Benjamin Brooks. The effort was successful and provided the land.

The construction was difficult and a combination of rail rate regulation and an economic downturn had starved the project for cash and stalled construction for years, in the difficult ground south of Santa Margarita.

As the end of the 19th century approached, the railroad gathered itself to complete the last unfinished major line.

When the Tribune picked up an 1893 story from the San Francisco Examiner announcing resumption of construction, the Tribune excitedly predicted the first train would arrive from Santa Margarita in spring. The guess was off by a little — a year and five days.

In 1893-94, workers blasted 1,100,000 cubic yards of rock from under the Santa Lucia Range. The September 21, 1950 edition of "Engineering News-Record" called the work: "a world's record for hand-drilled tunnels that may well still be unbeaten today."

By way of comparison, excavation for Hoover Dam footings was only slightly larger, at 1,500,000 cubic yards. Add in rock from the later daylighting of two tunnels and enlargement, by almost a quarter, of the remaining tunnels in the 1940s, and the amount of rock moved is similar.

Serpentine rock is relatively soft and easier to drill than the granitic Sierra Nevada. However, the brittle and fractured stone required careful reinforcement to prevent collapse. At least two men died during construction.

The former sea floor, now mountain, has been sometimes described like a sponge, with underground pockets of rainwater-fed springs. Near the edges of ridges, the hill was prone to slip as construction changed eons of balance.

According to a chapter in the book "The Achievers" by Edson T. Strobridge and Loren Nicholson, the highest point in the Coast Line between San Francisco and Los Angeles was difficult terrain. Southern Pacific's veteran chief engineer William Hood said of the task: "the tunnel work on the Cuesta Grade is harder than the case in the Siskiyous." 

According to the book "Southern Pacific's Coast Line" by John R. Signor, it was the most costly 17 miles of the line. The path from Santa Margarita to San Luis Obispo included seven tunnels in the the original design. Signor quotes the Oakland Tribune estimating the cost at $3 million, other sources from the time — including the San Luis Obispo Tribune — placed the cost at $1.5 million. Either way, it would not be cheap.

Apparently not all the drilling was done by hand. The railroad had portable compressed air and diamond drill equipment that had been used building the northern route.

At the peak of construction, 1,200 men were at work on the project. Some work crews were Chinese. In February 1893, electric lights powered by a railroad generator replaced tallow candles. Construction went around the clock.

The longest tunnel, No. 6, was 3,610 feet long. To save time, excavation was started from both sides.One route was curved followed by a straight section; the other had an "S" shape. Both excavations traveled uphill and met within a quarterinch. Rails were shaped in the Oakland railyard to a 1/32-inch tolerance and delivered to the site.

In addition to the tunnels, a major steel trestle was built at Stenner Creek before the Southern Pacific arrived in San Luis Obispo. The rail line outgrew the original 14-foot-wide, 18-foot-tall tunnel openings.

By 1940, expansion started; the original tunnel construction had taken about 17 months, while expansion took 12 years. The railroad could not afford to shut down the single track mainline for construction.

Progress was about 8 feet a week.

The new structure would be two feet wider on each side with straight walls rather than keystoning outward at the top. The new height would be 6 1/2 feet taller, with more room for smoke to clear.

Many of the redwood timbers were from the original construction, blackened by soot from 50 years of oil-fired steam engine travel.

Each hole required only half a stick of dynamite per shot, and each of the up to 40 holes was detonated separately. The claustrophobic work could not be allowed to damage the timbers.

On Jan. 11, 1962, the Telegram-Tribune reported that the nearly 900-foot long Tunnel 10 was being bypassed by Southern Pacific at a cost of $120,000. The boarded-up tunnel can still be seen from the highway.

Using modern heavy earth-moving equipment, the job likely took less time than the tunnel excavations took. It was expected to be finished in February of that year.

On March 20, 1968, it was reported that slippages and slides from subsurface water were damaging the line. Holes were being drilled to pipe out the water.

By 1979, the number of tunnels had been reduced to five, with a combined length of a little over a mile.

One tunnel was daylighted in 1910 after it collapsed. Oddly, newspaper articles at the time also call this tunnel 10, so at some point the numbering system must have changed. Perhaps a more diligent student of local railroad history can explain the anomaly.

• • •

The Central Coast Railroad Festival will take place Oct. 10-14 with the opening of the new San Luis Obispo Railroad Museum.

The Tribune is pleased to provide this opportunity to share information, experiences and observations about what's in the news. Some of the comments may be reprinted elsewhere in the site or in the newspaper. We encourage lively, open debate on the issues of the day, and ask that you refrain from profanity, hate speech, personal comments and remarks that are off point. Thank you for taking the time to offer your thoughts.

Commenting FAQs | Terms of Service