Subterranean Continental Divide

On November 20, 2011 · 8 Comments

I have a fascination with tunnels and I’ve featured them before on the Twelve Mile Circle including articles on Superlative Tunnels, Tunnel Under the Border, and Tunnels, Bridges, Lifts and Inclines. I’ve also fixated on boundaries and watersheds previously such as the Hydrological Apex of North America.

It seems odd to me that I hadn’t yet encountered a mashup of the two, yet that’s exactly what occurred when I read an article in Slate a few weeks ago. The article wasn’t about tunnels or watersheds precisely. Rather it focused on traffic efficiency versus driving speeds, including the counterintuitive notion that "sometimes you have to go slower to go faster." Colorado throttles Interstate 70 speeds down to 55 miles per hour west of Denver at certain levels of congestion using police cars as rolling roadblocks. It’s an interesting concept and you can read the article on your own if you prefer because it’s not actually germane to this conversation. I latched onto a single phrase… "a two-mile-long tunnel that dips under the Continental Divide."

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You read that correctly. It’s possible to drive across North America’s continental divide below the surface. Technically this is the Great Divide, one of several "continental divides" albeit the most well-known version and generally the one that’s meant when someone mentions a divide without qualifiers. It’s pretty cool even with the asterisk, don’t you think?

It required a little fact-checking because it sounded almost too good to be true. The Colorado Department of Transportation believes it. They constructed the Eisenhower Tunnel in two phases in the 1970’s, the Eisenhower Memorial Bore for westbound traffic and the Edwin C. Johnson Memorial Bore for eastbound traffic. CDOT throws out a number of superlatives as they describe their engineering achievement:

It is the highest vehicular tunnel in the world, located at an elevation of 11,013 feet at the East Portal and 11,158 feet at the West Portal. The Tunnel traverses through the Continental Divide at an average elevation of 11,112 feet… Annual snow fall in the area averages 315 inches (26 feet) for the months of November through April.

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Crossing the Rocky Mountains isn’t a joke. The Eisenhower Tunnel burrows beneath a summit that climbs 12,500 feet (3,810 metres). An Interstate highway could not possible cross here without a tunnel. Previously vehicles twisted around the southern edge using Loveland Pass at speeds considerably lower than Interstate standards, adding another hour to their passage.

The tunnel entrance at 11,000+ feet is still amazing. I’ve never used this tunnel although I crossed the Great Divide further north during a visit to Rocky Mountain National Park. That’s an elevation high enough to cause one to become light-headed until acclimated, as was the case for myself who lives practically at sea level.

What would happen if a bottle of water happened to fall from one’s vehicle at whatever point in the tunnel marks the divide? It would probably break and evaporate but for the sake of amusement lets say it happened right on the divide and water flowed unobstructed in both directions without soaking into the ground, etc., etc., etc. The eastern water would travel Clear Creek –> South Platte River –> Platte River –> Missouri River –> Mississippi River –> Gulf of Mexico –> Atlantic Ocean. The western water would travel Straight Creek –> Blue River –> Colorado River –> Gulf of California –> Pacific Ocean.

Clear Creek is quite famous as the epicenter of the 1859 Colorado Gold Rush. It also passes through Golden, CO, the home of the Coors brewery. A few molecules of our hypothetically spilled liquid might possibly make its way into the Rocky Mountain Water touted by the brewery (or be contaminated by it). Straight Creek isn’t nearly as famous and faces it own set of issues. The I-70 corridor takes a toll on the surrounding countryside. CDOT dumps huge amounts of sand on the roadway to keep it open during the winter which then washes into the creek as silt.

I became aware of other tunnels under continental divides during my search and perhaps I will elaborate on them someday. Until then, feel free to explore on your own:

Totally Unrelated

I enabled the new MapsGL this morning in Google Maps. It seems like Google is bringing Maps a bit closer to Google Earth (without requiring the plugin). I’m not sure I have any immediate reactions other than to notice that it hasn’t required any great mental adjustments on my part.


On November 20, 2011 · 8 Comments

8 Responses to “Subterranean Continental Divide”

  1. Pfly says:

    Another place I’m familiar with! I lived in Denver for several years and took lots of random road trips into the mountains. Been through the Eisenhower Tunnel many times–although the old, twisty road over Loveland Pass is way more exciting! Also, you can ski over the tunnel. Loveland Ski Resort is on the east side slopes over the tunnel. I only skied there once–working out at 10,000+ feet elevation is no fun for me.

    As for water flowing from the divide at or near Eisenhower Tunnel, it may not be so simple. Water flowing west would end up in Straight Creek, yes, but only some would flow into the Blue River. A significant amount is diverted to Dillon Reservoir and piped east back under the divide to supply Denver with municipal water. And a good amount of the Blue River is diverted back under the divide via the Colorado-Big Thompson Project. …just saying!

    Also, I-70 west of Denver in the mountains has a whole series of features unusual for an interstate. As I understand when it was built a whole bunch of special exceptions to the federal interstate standards had to be made. Besides the tunnel there’s at least one very sharp turn and places where the west and east bound lanes are stacked atop each other or switch sides. It’s definitely a fun stretch of interstate, especially going west–after the endless flatness of the plains suddenly *blam*, extreme mountains.

  2. Joe says:

    I couldn’t decide whether to post this under this post or under the previous post, but since I had already chimed in on the previous post and my search was started because of this post, I settled here. Anyways…

    I started checking links and reading up on the tunnel. Eventually my reading led me broader information about the area which then led to this site: The post appears to be from a native of Denver, CO and documents his journey to several other Denver cities, most of which are little more than a dot on a map. Nothing earth shattering, but just another example of how all of these article are interrelated.

  3. Mike Lowe says:

    I have travelled through that tunnel several times in the last decade. This here engineer loves it. The approaches are fun too.

    I can’t profess that your spilled water trick will work. As far as I recall, the tunnel has a constant slope. I imagine that allows water and air and exhaust to drain with the help of gravity. Huge fans help too.

    I highly recommend Loveland Pass. It’s a fun twisty road with my turbocharged vehicles and the summit has a scenic view of the area immediately around the tunnel. Some couch exploring with Google Maps can be fun and use Terrain View for the countour line fun.

    The stretch of I70 through Glenwood Canyon is great. There are good articles online about the exceptional civil engineering. Really, I’d rate all of I70 between Golden and Grand Junction as very nice indeed. Of course that is coming from a flatlander Houstonian. 🙂

    • Rhodent says:

      I was wondering when I read the article whether there was a slope in the tunnel that would play with the Divide. If you think about it, this means that there’s a place where you can be on one side of the Divide but another person standing above you would be on the other side. There can’t be many places like that.

      • According to the signs posted at the Tunnel approaches, the west entrance is 145 feet higher than the east entrance. So Rhodent is right: any water in the Tunnel would (theoretically) drain into the Atlantic watershed. Yet another example of how those crafty Denverites steal water from the Western Slope…

  4. Ken Saldi says:

    I have lived in Colorado most of my life and have traversed this tunnel many, many times. It is quite the marvel, but here are a few things that have not been mentioned.
    1. In case you were wondering, there is a sign for the continental divide on both sides of the tunnel, approximately half way through.
    2. It is the highest section of interstate highway in the US.
    3. In Colorado, everyone calls it either the Eisenhower Tunnel or just the tunnel; no one mentions the Johnson side.
    4. The Eisenhower side got opened first and there originally was 1 lane in each direction, while they bore the Johnson tunnel.
    5. While you can notice the slope going in and out, there is no apparent apex, just a gradual top point.
    6. During bad weather (ie when Loveland Pass is closed), they close the tunnel from 50 past the hour for 10 minutes to let hazardous materials trucks through. They then open it up to normal traffic for the remianing 50 minutes.

    I remember once I was going east through the Johnson Bore and it was snowing hard. It took me 2 hours to go the last 4 miles up to the tunnel (it is very steep on that side). When I got through to the eastern side, the ground wasn’t even wet and it was about 25 degrees warmer.

    As for Pfly’s comment, in Glenwood Canyon, the west bound lanes are higher in the canyon and sometimes go over the east bound lanes, though it never fully covers the lanes. There are no sections of I-70 in Colorado that switch sides however. There is a section where US Highway 6 merges with I-70 after Golden (it merges with I-70 in Denver, leaves to take its own route through the foothills and then remerges with I-70 after Golden) where there is nearly a 90 degree turn and the speed limit goes to 35 (I think). There is also a very sharp turn right next to Parachute (near Grand Junction) that slows down to 55 because of a sharp curve.


  5. Jasper says:

    If you want tot cross the Continental Divide in many different places close together, go to Yellowstone. I also discovered there that the border between Idaho and Montana follows the Continental Divide for quite a bit.

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