I recently returned from a trip to the western Arizona and eastern California portions of the border with Mexico, where I had the opportunity to view the fences and other barriers that have been erected between the two countries. The architect Louis Sullivan famously remarked that "form follows function", and that is applicable in its truest sense in the manner in which the specific style of barrier that is being used at different parts of the border matches the purpose for which it was erected.

In and around urban areas that are separated by walls (Mexicali, Mexico, and Calexico, Calif.; Los Algodones, Mexico, and Andrade, Calif.; and San Luis Rio Colorado, Mexico, and San Luis, Ariz.), the most common kind of wall was constructed from surplus Vietnam-era landing mats (corrugated metal sheets used for temporary airstrips). Here is an example from the Andrade side:

As you can see, the landing-mat wall is topped with razor wire, which was recently installed in order to prevent illegal border-crossers from traversing the wall.

On the Los Algodones side, the locals have put the wall to good use as advertising space:

The portion where the sandy dirt has been dug out revealed a concrete footer under the wall. Nothing could be passed through the wall, and crossing over the wall would have been a futile and dangerous endeavor: Border Patrol regularly kept watch on the U.S. side:

That wall was put to different use in San Luis Rio Colorado, Mexico. Here are migrants camped up against the fence awaiting the opportunity to make credible fear claims at the San Luis Port of Entry:

Bollard-style fencing separates the border in more remote areas. Here is an example of such fencing on the outskirts of San Luis, Ariz.:

The gates allow Border Patrol vehicles access to the road on the other side of the fence.

In the desert east of San Luis, I saw a more substantial bollard-style fence, consisting of posts and solid steel panels:

The arrows point to spots where a group of migrants recently tunneled under the wall. As AZCentral reported that incident:

The largest single group of migrant families and minors ever recorded in the Yuma area tunneled underneath a border fence and voluntarily turned themselves in to U.S. Border Patrol agents, according to Customs and Border Protection officials in Arizona.

A group of 376 migrants, composed almost overwhelmingly of Guatemalan families and children seeking asylum, breached the U.S.-Mexico border just before noon Monday, approximately 4½ miles east of the San Luis commercial port of entry.

There were no concrete footers under that part of the wall, and the ground was sandy. Small holes in the wall are there to allow animals to pass through:

That said, the landscape on the U.S. side of the border was barren and forbidding:

Not visible is the closest structure: the Arizona State Prison Complex on South Avenue B, which can barely be seen in this picture, along with a camera tower in the distance. Border Patrol "drag marks" crossed the "road", revealing where vehicles and individuals had passed:

Thinner post fences sat directly adjacent to the ports of entry, again surrounded by razor wire. Here is the post fence at the port-of-entry in Calexico, Calif.:

Similar, but slightly shorter, fencing is installed at the Andrade, Calif., port of entry, separating it from the Alamo Canal:

And here, surrounded by razor wire, separating the port facility in Andrade from Los Algodones:

Metal mesh fences are also used, usually as a second-line fence, as here in Andrade, where they separate the Border Patrol access road from a nearby parking lot:

Two different styles of metal mesh fences, one topped with razor wire, and the other topped with barbed wire, surround the Border Patrol access road near the San Luis Port of Entry:

Similarly, metal mesh fences surround the bridge over the All American Canal in Gordons Well, Calif.:

Gordons Well is in a particularly remote part of the border. That area features brace and beam anti-ram fences along the border itself:

In addition, there are also brace-and-beam anti-ram bollard fences with gates at Gordons Well:

In addition to fences, there are also vehicle barriers along the border. Here is examples of so-called Normandy barriers near Yuma:

In addition, concrete barriers topped with razor wire are available to be placed near the San Luis port of entry, in the event of a mass rush of individuals through the port:

And here, near the Andrade port of entry:

Finally, visible in the right-side background of this photograph from the port of Andrade are simple tubular vehicle barriers.

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