Whenever I drive across New Mexico, I’m on the lookout for a little sign by the side of the road unceremoniously announcing "Continental Divide"–a sign like the one on the left (only that one’s actually in North Dakota rather than New Mexico).
Growing up, I had the idea that the continental divide was a the highest mountain ridge on the continent so that it divided the continent into two sides that sloped away to the ocean.
Well, that and it was a John Belushi movie.
But if you go and see the continental divide, you may find that you’re not at a mountain ridge at all. There may not even be a mountain ridge in sight. Where you are may be flat.
That’s the way it looks at the continental divide in New Mexico, and it looks pretty similar at the location in North Dakota.
Even more confusingly, when you’re at the continental divide there can be higher points of land on either side of it, within sight.
What’s the explanation?
The explanation is that the continental divide isn’t a ridge made out of the highest land on the continent. It’s an elevation of land that separates two watersheds, so that rain falling on one side of it will tend to find its way toward one ocean and rain falling on the other side will tend to find its way to another.
That means that the continental divide will tend to be high ground, but it doesn’t all have to be mountainous (it can be in relatiely flat countryside) and it doesn’t have to be the highest thing in the area. There can be higher points on both sides, there just has to be a depression between the higher point and the continental divide so that the flow of water toward the ocean isn’t thwarted.
Now here’s a new twist: There isn’t just one continental divide in North America. There are four (click to enlarge).
The one everybody thinks of as "the Continental Divide" is actually the Great Continental Divide, but there are three others, depending on what body of water a watershed is sloping toward–whether it’s the Pacific Ocean, the Arctic Ocean, the Labrador Sea, the Atlantic Ocean, or the Gulf of Mexico.
I was surprised at how much of the United States is in the watershed leading to the Gulf of Mexico. I’d kind of assumed that water on the east sid of the Great Divide would flow toward the Atlantic, but oh yeah, there’s another bunch of mountains in the way, so it’s going to go down into the Gulf.
Other continents also have continental divides, though they’re not always as clearly demarkable as they are in North America, so GO NORTH AMERICA! We’ve got FOUR, CLEARLY DEMARKABLE divides!
Of similar interest, there is a hill in central Colorado, from which water flows to three completely different entry points in the ocean/gulfs/etc. The author of this website was successful in having it named “Headwaters Hill”. Go there for more info!
I feel constrained to point out that “clearly demarkable” is, to a certain extent, a matter of opinion and open to subjective determination. It seems especially questionable to me that the Gulf of St. Lawrence should get its own contintental-level watershed. IMO, the western portion of the “St. Lawrence Divide” should be considered an extension of the Eastern Divide, and the eastern part of the St. Lawrence should simply be eliminated.
Living in central PA, I am pretty close to the “confluence” of two divides which divide the Gulf, Atlantic, and St. Lawrence drainage basins. I pass close to the area whenever I head up to visit my Ma in Buffalo. I imagine a hilltop somewhere near the NY/PA border where a drop of water, by minutely changing where it lands, could end up in New Orleans, Baltimore, or somewhere off the coast of Labrador.
San Diego county has a minor water divide separating coastal watersheds to the pacific ocean from inland watersheds to the gulf of california. For more info:
http://www.waterboards.ca.gov/sandiego/
The map:
http://www.waterboards.ca.gov/sandiego/programs/basin_plan/SAN%20DIEGO%20RWQCB%20BASIN%20PLAN%20MAP.pdf
great jimmy. i used to watchf or them always too, btu i had nio idea i live on one (well, sort of, since it all ends up in the Atlantic) here in SE MICH. thx!
Theres a great point in a story by Norman Maclean (author of A River Runs Through It) where he talks about as a teenage boy standing atop a ridge in Montana and peeing on two sides having them flow to two different oceans! A bit crude but to this old hick still funny!
Back to the main topic – on Interstate 68 in western Maryland the Eastern Continental Divide is clearly marked. I believe it’s west of Cumberland. I’ve crossed that point many times on drives through Maryland.
…and Minnesota is the only state with 3 watersheds – GO MINNESOTA!
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…and Minnesota is the only state with 3 watersheds – GO MINNESOTA!
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When Minnesotans pee, they pee all over the place.
The “Grand Divide” in northern Missouri and Iowa separates the watersheds of the Mississippi and Missouri Rivers. The streams and ridges of that area have a remarkable trend, all running parallel with each other from north to south. Since no rivers cross the Divide, this was an ancient road, used by natives, pioneers, and the first railroads. It was also the site of the Honey War between Missouri and Iowa Territory.
Calhoun County, Illinois, although very close to Saint Louis, is a perfectly rural and profoundly beautiful area, mainly due to the Dividing Range that separates the Mississippi and Illinois River watersheds. That is a very prominent, high ridge that takes up most of the land area of the county. That makes the land bad for agriculture, and a lack of bridges keeps out suburban sprawl. Locals tell me that the Illinois River there is perfect for boating, and you can wade across it (except for the fact that it’s Chicago’s sewer).
…and Minnesota is the only state with 3 watersheds – GO MINNESOTA!
Well, not exactly. Montana spoils that as the Northern watershed dips into Glacer National Park and meets the Great Divide at Triple Divide Peak. (Guess why it’s called that?)
Everything makes so much more sense to me now that I’ve read this article. Well, okay, not everything, but at least the fact that when I drive through Waukesha county, just a few minutes west of Milwaukee-essentially the least likely place in the continent for a continental divide-lo! and behold there is a continental divide.