Among officials at the construction site Tuesday was Assistant San Diego police Chief Dave Nisleit and a Border Patrol spokesperson from Washington.
The man, who said he was from Chiapas, Mexico, was detained by agents as they prepared for a news conference to announce that contractors have begun building eight prototypes of President Donald Trump's proposed border wall with Mexico.
In a video taken by the NBC 7 News helicopter, a photographer captured images of dirt being graded by tractors, and rectangular cutouts, presumably where the prototypes will be built.
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The prototypes CBP solicited called for a wall about 30 feet tall, one made of concrete and the other incorporating potentially alternate materials with a see-through component.
"We are committed to securing our border and that includes constructing border walls", said Ronald Vitiello, acting deputy commissioner of U.S. Customs and Border Protection.
Agents - and Mr. Trump - say visibility through the wall is critical for knowing what's going on in Mexico, helping agents avoid ambushes or other potential dangers, as well as spot migrants or smugglers preparing to try to cross.
The US President had promised a "big, handsome wall" at the border with Mexico. "It may be a combination of designs being implemented". Both waivers are in California, including one that covers the site of prototype construction. However, Congress is yet to approve the first £1.11bn portion of funding requested by Trump to begin construction of the full-length wall.
The top designs for a concrete wall came from four companies: Caddell Construction Co (DE), LLC, of Montgomery, Alabama; Fisher Sand & Gravel Co., DBA Fisher Industries, of Tempe, Arizona; Texas Sterling Construction Co., of Houston, Texas; W. G. Yates & Sons Construction Company, of Philadelphia, Mississippi.