As @USBPChiefYUM explains, this section of fence was erected in the 90’s. It’s made of “landing matte,” a Vietnam era surplus originally manufactured as landing pads for helicopters in the wetlands of Vietnam:
Here @USBPChiefYUM describes some of the vulnerabilities of this design.
The angled top doesn’t allow anyone to shimmy down the north side, but it also makes for an easy place to hang out until border patrol leaves the area.
He also notes that it will be replaced this year:
As @USBPChief describes, the old design didn’t allow agents to see the other side, so large groups could assemble without Border Patrol’s knowledge.
He compares that to the new construction, which is see-through but also offers protection for border agents: