Cartels have had FOBs in Arizona for some time now so this is not surprising. It is an escalation though leading up to perhaps open conflict between Border patrol and Cartel forces. From KVOA:

In this Crime Trackers investigation, Lupita Murillo and photographer Kean Bauman were given unprecedented access to a special camp along the US/Mexico border.

As more manpower and resources are dedicated to protect the border, agents are setting up camps that take them closer to the action. They’re called Forward Operating Camps.

These agents are stationed in rural areas known as “hot spots” to respond quickly.

In this Crime Trackers investigation, you’ll see agents in action, and the remoteness of where they work.
In rugged terrain in the harsh Southern Arizona desert, Border Patrol agents quickly move to find illegal activity.

Agent Jorge Sanchez says, “The scope operator had a visual of large back packs, that’s what we saw.”

We’re in an undisclosed location to protect the agents who sign up for the extra duty– they’re here a week at a time in this Forward Operating Camp. The camp is self contained, powered by generators.

Agent Brian Irving says, “To have a remote camp set out here for the traffic that crosses is very important.”
Important because it cuts down the driving time agents have to go through to get here.

Agent Jason Rheinfrank says, “Agents can respond before a lot of this illegal activity gets north and they load up into a vehicle and make their way up to Tucson and Phoenix.”

This assignment is equally dangerous.

Agent Irving says, “I’ve come across an armed group, it wasn’t out here at this camp it was at a different location.”

Agent Sanchez says, “You never know if they are armed they could have rifles or guns with them.”

This is probably partially driven by high gas prices making the old model of driving hundreds of miles a day impossible, but it’s also a sign that the Border Patrol is taking the war on the border more seriously and adjusting their tactics from a law enforcement stance to a more militarized stance.