Conquering the Continental Divide: The Epic Push for Interstate 70

Rowan Hart

Start with a road. U.S. Highway 6 climbs over Loveland Pass west of Denver. William Loveland built a wagon road over that mountain in 1879, and the first automobile didn't cross until 1929. The State Highway Department paved the route in 1950. So picture a driver on that pavement in winter, trying to get over the Continental Divide with the weather in charge.

Rowan Hart

I can't give you one particular driver's diary, because the sources I have don't contain one, and I won't make one up. What the Colorado historical marker in Georgetown does say is blunt: geography and weather placed strict limits on travel routes and seasons. It calls the road slow and winding. When a tunnel finally replaced it, the tunnel saved motorists 9.1 miles of that road. Meanwhile the Western Slope's farmers needed reliable, year round routes to Denver markets and railroads, and Colorado's tourism industry wanted better highways. A road that the weather can shut down is a bad answer to both.

Rowan Hart

This episode is about the answer Colorado built, and about two places where building it got very hard. One is a hole under the Continental Divide. The other is a canyon on the Colorado River. But first we need to go back to the 1950s, to a map where the highway was supposed to stop.

Rowan Hart

So here's where we are. It's the middle of the 1950s. Congress has just committed the country to a national highway network, and Colorado is about to find out whether the Rocky Mountains are part of it.

Rowan Hart

The 1956 Federal Aid Highway Act authorized a network of forty thousand miles. According to the engineering magazine Civil Engineering, in an article from the American Society of Civil Engineers, the initial plan for Interstate 70 called for it to run west from Baltimore to Denver, and no farther into the Rockies. Denver was the end of the line.

Rowan Hart

Why? None of my sources states the federal reasoning outright, so let me separate what the record says from what I'm inferring. The record says Colorado had been trying to get a tunnel under the Divide for years and kept failing. In 1947 the state got exactly one bid, ten million dollars, which was far in excess of the engineers' estimate and was never formally considered. When the state advertised again that December, nobody bid at all. In 1956, the state opened bids on two tunnel projects, one at Straight Creek and one at Berthoud Pass. Each drew only one valid bid, and no contract was awarded. My inference is that a federal planner looking at that history might reasonably have seen a mountain nobody wanted to price. That's an inference, not a quotation.

Rowan Hart

Colorado did not take the hint. The Civil Engineering article says Colorado leaders quickly pressed for a route through the mountains, and that military officials wanted a route connecting the central United States with Southern California. And the state's marker names the man who led the push: Edwin C. Johnson, known as Big Ed. Three terms as a United States Senator, two terms as governor. The marker says he used his political savvy to convince the federal government to route the interstate through Colorado, and that his efforts broke a decades long stalemate over high country road construction.

Rowan Hart

There was pressure from the street too. Charles Shumate, who spent five decades with the Colorado Department of Highways, from 1924 to 1975, remembered the 1960s this way, and I'm quoting the marker quoting him: "50 to 75 cars going around and around the capitol building honking their horns and with signs saying, 'The Western Slope Needs to Tunnel Under the Continental Divide'." Fifty to seventy five cars. That's not a mass movement. That's a motorcade of people who were very tired of Loveland Pass.

Rowan Hart

Now the Utah side, because it matters, and it's the part of this story most people never hear. The state of Utah's History to Go site draws on Edward Geary's History of Emery County. In 1957, legislation sponsored by Utah Senator Wallace F. Bennett added a thousand miles to the original forty thousand mile system. Utah officials proposed that part of that new mileage connect Denver with the Wasatch Front, the metropolitan area around Salt Lake City. That's where Utah's people and money were.

Rowan Hart

Federal highway officials decided otherwise. They decreed that the new road should go more directly west from Denver and meet Interstate 15 at Cove Fort, in central Utah. The Colorado Department of Transportation dates the federal designation to October 1957. One thing I have to be straight about: the Utah source says federal officials decreed this. It doesn't describe Utah eventually agreeing in any formal sense. It describes a decision handed down, and then reactions.

Rowan Hart

The reactions split. Salt Lake City newspapers decried the new road as a "road to nowhere." The road would be the first major transportation link in Utah that didn't funnel through the Wasatch Front. But in Emery County it was, in the source's words, eagerly hailed as a long overdue recognition of the natural advantages of the Salina Canyon route.

Rowan Hart

And Emery County's story has an irony in it. County officials hoped the interstate would follow roughly the old Spanish Trail route, which would have put several county towns right on the highway. Then in the summer of 1958 they invited state and federal highway representatives on a two day safari through the San Rafael Swell, hoping to show off the scenery. The party traveled over primitive roads. According to Geary, it was apparently that trip that gave highway officials the idea of running Interstate 70 straight through the heart of the Swell. The result was arguably the most scenic stretch on the whole interstate system. But the direct economic benefits to Emery County were, in the source's phrase, largely limited to Green River.

Rowan Hart

The route across the Swell was surveyed in early 1963. It opened with a dedication at Ghost Rock on November 5, 1970, initially with two lanes, and the other two lanes took roughly a dozen more years. And the 110 miles between Green River and Salina still count as the longest stretch without services on the entire interstate system. A road to nowhere, the newspapers said. Well, it has a very long nowhere in the middle of it.

Rowan Hart

One more piece of the map. In March 1960, an engineering firm, E. Lionel Pavlo of New York City, looked at eight possible routes between Empire Junction and Dotsero in Colorado. It picked Straight Creek as the best, and argued a tunnel was needed because the Divide couldn't be crossed any other way while keeping interstate standards. Federal money for the Denver to Cove Fort leg wasn't available until the 1962 to 1963 budget. After that, the debate was over and the digging could begin.

Rowan Hart

Where we are now: the early 1960s. The route is chosen, the money is coming, and what's at stake is whether anyone can actually drive a highway tunnel through granite at eleven thousand feet. Remember, the state had already tried this and failed to attract a serious bid, three separate times.

Rowan Hart

The state first tested the mountain in the early 1940s. Between 1941 and 1943, the Department of Highways dug a pioneer bore under Loveland Pass. It was seven feet by seven feet and just over a mile long, which is a crawl space, not a road. It was eventually abandoned as road standards changed after 1945.

Rowan Hart

The real test came with a pilot bore along the Straight Creek route. A contractor, Mid Valley Incorporated of Houston, started in October 1963 and holed through on December 3, 1964. Charles Shumate, the veteran highway man, said in 1963 that the work was "the most difficult feat ever undertaken by the Colorado Highway Department." Remember, he's the guy with the quote for every reporter.

Rowan Hart

The pilot bore gave engineers numbers, and the numbers were encouraging. Of its length, 26.5 percent was rock that held itself up. The other 73.5 percent needed supports in varying degrees, and the total footage of what tunnelers call bad rock was 820 feet. That was the theory. The vehicle tunnel would sit between 115 and 230 feet north of the pilot, and Colorado's own account admits that conditions there did not exactly duplicate the pilot's, and that extrapolating from the pilot's stresses did not prove exact in every case.

Rowan Hart

Bids opened on October 3, 1967, the fourth call for bids on a highway tunnel under the Divide. The winner was Straight Creek Constructors, a joint venture of four companies: Al Johnson Construction of Minneapolis, Gibbons and Reed of Salt Lake City, Kemper Construction of Los Angeles, and Western Paving Construction of Denver. Their bid was $54,140,486. The state's own estimate had been $42,479,000. So even the winning bid was more than twelve million dollars over what the engineers expected, and everyone knew it.

Rowan Hart

Work started March 15, 1968, with a goal of three years. Then the mountain started to push back. The state's own history lists the obstacles. Men and machines labored at lowered efficiency at eleven thousand feet. Winter kept the working season outside the tunnel painfully short. The hole itself was to be about fifty feet high and forty five feet wide, which is bigger than the old methods had been built for.

Rowan Hart

Now, what did a shift feel like? The state's marker leans on a Denver Post description: inside the mountain, "sound becomes a physical torrent," water "leaks" from the rocks, and miners wore "grimy, rubber coated tub overalls." A second Denver Post line, from 1978, during the later bore, says: "This mountain leaks. If the pedestrian watches where he is putting his feet he finds cold water running down his neck." The work itself had four steps. Drill holes, load explosives, shoot, and muck out the broken rock into narrow gauge cars pulled by an electric locomotive. Do it again. At the peak, 1,140 people worked three shifts, twenty four hours a day, six days a week.

Rowan Hart

By 1969 the trouble was serious. The marker says everyone knew the mountain still moved along the Loveland Fault and that fragile rock could come down at any time. The contractors had a 450 ton mining shield, built to dig and hold up the rock at the same time. It moved only a few yards before loose rock and pressure seized it in its tracks. A machine the weight of a small ship, stuck in place by the mountain it was supposed to cut.

Rowan Hart

The fix came from the people who ran the job. Phillip McOllough was the Department of Highways' tunnel construction engineer from July 1968. R.C. Hopper, called Rube, was the district engineer. They went to what the marker calls the multiple drilling method. Crews dug thirteen small tunnels, called drifts, six to eight feet tall, in an arch around the edge of the big cross section. Each one was filled with concrete. They worked from the bottom of the arch up, so the concrete in the first drift became the floor of the next. When the arch was done, they could dig out the middle safely. Hopper's verdict, according to the marker, was that it was "a little slow, but it is foolproof."

Rowan Hart

And here's the line that tunnel people still quote. The Colorado Department of Transportation credits it to "one veteran highway engineer" and gives it as: "We were going by the book, but the damned mountain couldn't read." The state's historical marker attributes the sentence to Hopper, dated 1972, and prints it without the damned. So the sources agree on the sentiment and on the attribution to Hopper only in one place. I'll let you decide whether a state marker would clean up a swear word.

Rowan Hart

The money followed the rock. On December 16, 1970, the state changed the pay procedure on mining items from the original per item bidding to a cost basis, because of what it calls difficulties encountered in mid mountain. The marker says that changing the tunneling method because of bad rock doubled the cost. The state's closeout figure for the project, from preliminary engineering to the end, is about $108 million, and at the time that set a record for a federal aid single project. Federal aid covered 91.32 percent of it.

Rowan Hart

Now, you asked, or rather the outline asked, about the workers who died building this tunnel. I went looking. The sources I have don't say. No names, no dates, no count. The marker says only that McOllough's cautious work saved lives, and that in more than forty years of operation there has never been a fatal accident in the tunnels. That second fact is about traffic, not construction. So on construction deaths, the record in front of me is silent, and I'm not going to fill the silence with a number. If a ledger or a court record exists somewhere, it's not in these pages.

Rowan Hart

The tunnel opened on March 8, 1973. Five years instead of three. Governor John A. Love dedicated it with occasional snow flurries and temperatures in the mid thirties. He called it, quoting the marker, "the most effective answer to tying east and west Colorado together and opening the way West."

Rowan Hart

Before we leave the mountain, two things about people, because the engineering story can hide them. The first is the names on the tunnel. The second is a clerical error.

Rowan Hart

Start with the names. The tunnel was first called the Straight Creek Tunnel, after the valley at its west portal. In 1972 the Colorado legislature chose a new title and designated it the Eisenhower Memorial Bore. The marker explains why Eisenhower got the credit: he was an avid sportsman who started visiting Colorado shortly after the Second World War, and like any citizen he sometimes got stuck in traffic on U.S. Highway 40 between Fraser and Denver. As president, he signed the 1956 interstate law. That's what the state wrote. It doesn't claim that the traffic jams shaped the law, and neither will I.

Rowan Hart

The second bore, the eastbound one, was designed starting in July 1972, before the first one even opened. Kiewit and Brown and Root got that contract and began in August 1975. The low bid was $102.8 million. It opened December 21, 1979, and was named for Edwin C. Johnson, Big Ed, the senator and governor who had spent years leaning on Washington. A photo caption in the marker shows him with Eisenhower in the Oval Office around 1953. Another shows him at the tunnel worksite in the early 1960s, in the middle of a group of unidentified men.

Rowan Hart

So why does Johnson matter to this story? Because the record says that when the federal map ended at Denver, he was the one pushing for the mountains. The tunnel Eisenhower's name sits on exists partly because a Colorado politician refused to let a line on a map be the final word. The state gave the eastbound bore his name in 1979. Altogether, the twin tunnels took thirteen years and $220 million, and they stand at 11,158 feet, the highest elevation on the interstate system.

Rowan Hart

Now the clerical error. In 1970, the Department of Highways, by mistake, offered a tunnel engineering job to Janet Bonnema. The marker's phrasing is that a clerical error offered her the job. She took it, and the department's workplace changed. In 1972, a state constitutional amendment guaranteed equal rights for women, which the marker says superseded miners' superstitions about women underground. Eighteen months after she was hired, she went underground to do her work. About sixty workers walked out.

Rowan Hart

All but one returned the next day. That's the whole record. The state tells us a photo exists of Bonnema laughing with Hopper on her first trip into the tunnel, in 1972. What the sources don't tell us is what was said on the walkout, who the one holdout was, or how she felt. I'm not going to guess. What I can say is that sixty men put down their tools over a woman engineer doing measurements, and by the following day nearly all of them had picked them up again.

Rowan Hart

Where we are now: the tunnels are done or being finished, and the interstate has crossed the Divide. But the road still has a hole in it, west of the tunnels, in a gorge on the Colorado River. What's at stake is whether the last miles of Interstate 70 can be built through one of the narrowest, most visible canyons in the state without wrecking it.

Rowan Hart

Glenwood Canyon runs about twelve and a half miles. Its rock walls reach as high as two thousand feet. The Civil Engineering article notes that even the area's Utes had seen it as impassable, which is one sentence I'm going to leave at one sentence. A railroad, the Denver and Rio Grande, went through in 1887. A primitive dirt road followed in the early 1900s and was upgraded to a two lane paved highway, U.S. 6, in the 1930s. In 1940 U.S. 6 was extended across Vail Pass and through the canyon.

Rowan Hart

That worked for decades, but badly in one way. The shoulders were narrow and there was little else built beside the road. Quoting the Public Roads article by Karen Stufflebeam Row and colleagues: motorists turned off at informal pullouts to fish, picnic, or camp, leaving garbage, ash filled fire rings, and other debris within a few feet of the river.

Rowan Hart

Planning for Interstate 70 through the mountains began in 1960. In 1965, two tunnels were driven through Horseshoe Bend, about a mile east of Glenwood Springs, just beyond the canyon's west end, to avoid a sharp, hazardous curve. That work would become important evidence in the argument that followed.

Rowan Hart

Because in 1969 Congress passed the National Environmental Policy Act, and the rules changed. According to a 2019 report for the Colorado Department of Transportation by Mead and Hunt, the law required a multidisciplinary approach that drew on the natural and social sciences and the environmental design arts. It also required public hearings. The engineer John Haley, who wrote a history of the project, said that projects that might have started in one to three years could now take a decade or longer, with costs rising along with the delay.

Rowan Hart

The Mead and Hunt report adds that before the 1960s, the federal Bureau of Public Roads and state transportation departments gave little consideration to the environmental and scenic impact of highway locations and designs. Engineers drew their plans, calculated their costs, and expected a grateful public. Haley's own line, and I'll attribute it to him: "Engineers became acquainted with environmentalists. Many were shocked by the experience."

Rowan Hart

The fight was real, and it wasn't simply for or against. The Glenwood Springs Chamber of Commerce made a film in 1971 called Interstate 70: Where and How? Haley describes it as arguing that standard cut and fill construction could not preserve the canyon's rugged beauty, and it showed ugly cuts from interstate construction around Glenwood Springs as proof. Its answer was a technique used in Italy, where mountain roads sit on concrete spans well above the ground, leaving room for vegetation, wildlife, and people.

Rowan Hart

Then came the argument over width. Two lanes and forty eight feet, which most environmentalists preferred. Four lanes and fifty six feet, which was the initial recommendation. Or four lanes and sixty eight feet, which planners ultimately chose. The federal government wasn't ready to sign off at first. It told the state to look harder at alternate routes and to form a citizens' advisory committee.

Rowan Hart

One member of that committee, a local businessman named Mark Skrotzki, turned into a long term critic. He wrote a petition to Governor Richard Lamm, who served from 1975 to 1987, saying that it was impossible to put such a highway through the canyon without permanently scarring the several million year old geologic formations and further disrupting the Colorado River headwaters. He eventually enlisted the singer John Denver and former Interior Secretary Stewart Udall. According to the Mead and Hunt report, Denver once staged a media event where he threw a rock across the canyon waters to show how narrow the canyon was. It took him six throws to hit the other side.

Rowan Hart

Most residents of the Western Slope, the article says, concluded the project was going to happen one way or another, and it was best to work with planners to make sure the highway preserved the beauty of the canyon. The U.S. Department of Transportation granted final approval in 1979, and construction began in 1980.

Rowan Hart

The design response is where this stops being a road story. Two teams split the canyon. Gruen Associates, led by Edgardo Contini, an architect and engineer born in Italy, took the east end. Daniel, Mann, Johnson and Mendenhall, led by Joseph Passonneau, took the west. Contini's idea was elevated roadways, to protect the vegetation underneath. Passonneau terraced the alignment so the highway fit the narrow canyon, and used overhangs on top of retaining walls so shadows would soften the concrete and make the wall look shorter. The piers were tall single columns, mostly ten feet wide, with random deep grooves meant to echo the rock joints, and colored a warm tan or light brown. The magazine says the design also let wildlife cross underneath.

Rowan Hart

The centerpiece was a pair of tunnels four thousand feet long at the trailhead to Hanging Lake. Each was drilled from four faces, one at each end and two from an open cut in the middle. Then the cut was backfilled and landscaped so it would vanish. The crews blasted the portals along natural joints so they'd look like cuts that were already there. The rock near Cinnamon Creek was good, free of faults and groundwater, so engineers used grouted rock dowels, limited shotcrete, and a thin concrete liner. Haley says that first of its kind design cut heavy construction costs by twenty percent.

Rowan Hart

The canyon floor refused to behave like the plans. Engineers assumed bedrock was close to the surface. In places it was 125 feet down. At the east end, sixty feet of highly compressible clay lay under the roadway. Trapani, the Department of Highways project manager who oversaw construction, likened it to a tube of toothpaste, the ground squeezing out as soon as you added weight. Pile drivers were out because of boulders in the talus and the damage they'd do. A contractor tried pumping thousands of gallons of grout into one porous slope, and the grout simply disappeared. The fix was compaction grouting, a newer technique. Crews built a cemented wall around the footing, then pumped stiff grout inside at such high pressure that the ground surface heaved, which told them the voids were full.

Rowan Hart

Even surveying was a puzzle. In a canyon that tight, Haley wrote, the party chief couldn't see the rodmen without crossing the river. The crews adopted a new tool, Hewlett Packard's Total Stations, battery powered instruments that measured angles with light beams and no reflective targets. The project was also among the first to use posttensioned concrete slabs on a roadway, with cables run through conduits and tightened after the concrete cured. And a 105 foot tall, 350 foot long gantry brought over from France moved from pier to pier, assembling the deck from above, so the work didn't need to run machinery across the canyon floor. Twenty six flexible rockfall fences went up as well.

Rowan Hart

The end of the work also needs care. The magazine says the road opened on October 14, 1992, and completed what may be America's greatest public works project, the Interstate Highway System. Notice the may. But the Colorado historical marker's timeline has a different entry: 1984, the Department of Highways completes the last segment of Interstate 70 through Glenwood Canyon. Those can't both describe the same thing. I can't tell you from these sources which date means what, or whether the marker is referring to some other milestone. I'd say Glenwood Canyon is described as the last piece by the engineering magazine, with the hedge, and left unresolved by the state's own timeline.

Rowan Hart

The price tag, per the Colorado Department of Transportation as quoted by the magazine, was $490 million in 1992 dollars, or about $925.5 million in 2021 terms. That bought three tunnels, fifteen miles of retaining walls, and forty bridges and viaducts. Horticulturists created the state's largest nursery just to grow 150,000 trees, shrubs, flowers, and other plants for landscaping afterward. The project won more than thirty awards, including the American Society of Civil Engineers' 1993 Outstanding Civil Engineering Achievement Award.

Rowan Hart

So what did the corridor change? I'll stay with what the sources support. The Colorado marker says the completed tunnels linked eastern and western Colorado with a year round, reliable route, and it estimates about 310 million vehicles drove through from the late 1970s to the early twenty first century. The Western Slope's farmers had a path to Denver that didn't depend on a pass. Tourism had a highway. That's the documented part.

Rowan Hart

What my sources don't cover is the part you might expect me to say next, about ski towns, or the booms that came after. I don't have documents on that here, and an episode built on records shouldn't pretend it does. The one regional note I can offer is a small one: the tunnel's east portal sits in Loveland Basin, and the whole structure lies on Arapaho National Forest land, with no privately owned right of way involved.

Rowan Hart

The tradeoff, then, is visible in the record, even if nobody wrote it as a lesson. In the tunnel, builders drilled through the hardest granite and fault zones they could find, with 1,140 people on three shifts, and the state's own account says it took five years instead of three and about twice the expected cost once the method had to change. In Glenwood Canyon, the argument wasn't over whether to build. It was over how much of the canyon to give up, and how to make the road look like it belonged. The Public Roads authors called the result a network of viaducts, bridges, and tunnels through an extraordinarily narrow, environmentally sensitive gorge.

Rowan Hart

Haley called the interstate system the largest, most ambitious, and most successful public works project of all time. That's his claim, and the magazine repeats it approvingly. I'll just note that the other side of the canyon argument, Skrotzki's, was that you cannot put such a highway through there without permanently scarring the formations. Both of those were written by people who loved the place.

Rowan Hart

And the road that was supposed to stop at Denver, the one Salt Lake City papers called a road to nowhere, did get built. Its tunnel at the Divide has never recorded a fatal accident in more than forty years of operation. A nursery grew 150,000 plants to cover the scars in a canyon. And out in central Utah, 110 miles lie between Green River and Salina with no services at all, the longest such stretch on the entire interstate system, which is still how the road to nowhere reads on a gas gauge.