Yuma Anomaly

On December 11, 2012 · 6 Comments

I received an email message the other day from a first-time reader who happened to stumble across 12MC randomly through a search engine, hoping to learn the answer to a burning question. I’d never covered the topic on the site before so I didn’t have a ready answer. It fascinated me though and of course I dropped all of my other research topics underway to pursue it further because I have a short attention span and I love to follow tangents. I put as much effort into the question as I’ve done for any article I’d post ordinarily so I might as well share the results with the rest of you.



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The reader who went by "James" recalled an anecdote from the not-too-distant past. He was traveling through Yuma, Arizona and wanted a bite to eat. Sometimes it’s tough finding a decent meal on the road and we all have our own ways to deal with that. I like to go to brewpubs under the theory if the food falls short at least the beer will be decent. James homes-in on casinos for the buffets. I hadn’t thought of that option before so I’ll have to add that to my travel tip list.

Anyway, he crossed the Colorado River — the border between California and Arizona — only to discover a small chunk of Arizona on the "wrong" side of the river with the state line running through the casino parking lot. It’s the Paradise Casino owned by the Quechan Tribe (formerly known as the Yuma Indians). I don’t believe it was an issue of legality since there are Native American casinos in California, too. However it’s not particularly germane to the anecdote so I’ll leave the question of this particular state-hugging casino alone. The more important aspect was the sliver of Arizona within territory one would ordinarily expect to belong to California.



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One is able to appreciate the full extent of the anomaly by zooming out the map a little further. Rivers don’t normally flow at right angles so it’s not like the current state border followed an old riverbed that changed over time. Why, James wondered, did this artifact exist?

I had no idea. I thought it might trace back to old Fort Yuma, constructed in the 1850′s on the California side of the river to protect the new settlement on what was then the New Mexico Territory. That was an interesting bit of history, however, it didn’t provide an explanation.

The answer turned out to be much more recent: March 12, 1963. It seemed crazy that two long-standing states (California since 1850 and Arizona since 1912) were still arguing over their common border as recently 1963 since it was supposed to be the Colorado River, and yet that was indeed the case. That’s when the two finally agreed upon an "Interstate Compact Defining the Boundary Between the States of Arizona and California." The United States Congress approved the Compact in 1966, thereby enshrining the odd jog in the border permanently. The Compact explained its logic:

The boundary between the State of Arizona and California on the Colorado River has become indefinite and uncertain because of the meanderings in the main channel of the Colorado River with the result that a state of confusion exists as to the true and correct location of the boundary, and the enforcement and administration of the laws of the two states and the United States have been rendered difficult.

It also provided, in excruciating detail, 34 points forming the new border in perpetuity (e.g., "700 feet to Point No. 28, which lies on the easterly shoulder line of said north-south road due east of the northeast corner of the stone retaining wall around the Indian School Hospital…"), along with requirements for another 234 subpoints not monumented.

This was elaborated upon further in a U.S. Geological Survey Professional Paper published by the Government Printing Office, "Boundaries of the United States and the several States." The key reference can be found on Page 153.



Because determination of the position midchannel at the time California entered the Union would be difficult now, it was decided to place the boundary line in a position that would provide an equitable distribution of the land that had been affected by the movement of the riverbed.

A map found on the following page (Page 154) clearly showed the jog.

How the two states agreed that this particular block should become part of Arizona may never be known except to those involved in the 1963 negotiations. Was it because it was close to Yuma? Was it because it was easy to reach from the rest of Arizona? That remains unanswered. However it was clearly intended to compensate Arizona for changes in the course of the Colorado River that had not been well-documented over the prior century. It was an approximation so straight lines and right angles were appropriate and probably easier to survey.

Thanks James, and I hope you become a regular reader.

On December 11, 2012 · 6 Comments

6 Responses to “Yuma Anomaly”

  1. Mr Burns says:

    The book you referenced interested me, so of course I had to check out the boundaries of Kansas. On page 139, I found this: “It is noteworthy that Kansas was the first state to be admitted to the Union having a meridional boundary referred to the Washington meridian.”

    The western boundary of Kansas is defined as falling on the “twenty-fifth meridian longitude west from Washington.” Since the Washington meridian has had it’s share of coverage on 12MC, I thought you might find it noteworthy, as well.

    • I do! — for two reasons. First the obvious, its association with the old American Meridian. Second because they used the word "meridional" (i.e., along a meridian) which one doesn’t get to see in print very often.

  2. Scott Surgent says:

    The AZ-CA compact would explain most of the river-boundary but not the small bit of Arizona on the west side of the Colorado River. It may have to do with the desire to keep the confluence of the Gila River with the Colorado River within Arizona’s boundaries. The rivers themselves, especially the Gila, become very broad, shallow and braided and it can be tough to glean the boundary clearly.

  3. Bill Cary says:

    The Yuma area anomaly pales in comparison to the border jogs between Texas and New Mexico at El Paso. If you take a look at the border via Google maps you’ll note several east-west / diagonal jogs on both sides of the river. Some of the jogs seem to travel around individual farms and what you would think is in New Mexico is actually in Texas.

    One strange jog on highway 28 and highway 260 juts into New Mexico only to be followed by a more unusual and invasive jog to the east into Texas’ territory. If you were to drive south on Westside Drive you would cross the border between the to states at least four time in a couple of miles (providing that Google maps is correct). I do have to wonder how these crossings are signed at the borders and if the locals know where the border truly lies.

  4. Fritz Keppler says:

    Or the meanderings of the Mississippi, especially the delta area south of Cairo IL. Last month I was in New Orleans for Christmas, so I took a ride to Mississippi to get in a few more county lines (including the quadripoint at Hancock/Harrison et al, and the short line between Lincoln and Walthall Counties). I tried to get to the large but thin meander where Tensas LA and Adams and Jefferson MS meet, but the road became too muddy for my car to traverse, I’ll have to try again in drier weather. These meanders afford a fair amount of dry land state and county line crossing in places where one would otherwise need some type of watercraft.

  5. Jeff Nibert says:

    Speaking of border adjustments being made because of changes in the course of a boundary river, I am wondering if anyone knows the exact locations of two “cuts” that Mexico ceded to Arizona in 1928 under the “Banco Convention of 1905.” That treaty was used to maintain the actual course of the Rio Grande as the U.S.-Mexico boundary by swapping from one nation to the other the “bancos” (or “cuts”) in the river’s meanders and oxbows when the river changed its course. After such a cut, land that had been on the Texas side of the Rio Grande would then find itself on the Mexican side of the river, and vice versa. These cut areas were officially given to the other nation in order to keep the Texas side as Texas and the Mexican side as Mexico. Between 1910 and 1976, 245 bancos were swapped along the Rio Grande, a low-lying alluvial river. The treaty also applied to the short Mexico-Arizona border along the non-alluvial Colorado River. There were only two cuts ever swapped there, both in 1928. Mexico handed both of them (842 acres in all) over to Arizona. It would be very interesting (to me, the banco geek) to pinpoint these two locations in Arizona. Anyone have an idea on how to locate them?

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