Customs and Border Protection is replacing a little more than two miles in downtown Calexico, a sliver of the president's plan for a "big, beautiful wall" with Mexico. A barrier built in the 1990s from recycled metal scraps and landing mat will be torn down for bollard-style posts that are 30 feet high, significantly taller than existing walls.

The administration is seeking $18 billion to extend the wall. Efforts to pay for it as part of a broader immigration package that would include granting legal status for people who came to the county as young children failed in the Senate last week.

In November, SWF Constructors of Omaha, Neb., won a contract for $18 million to replace the wall in Calexico, about 120 miles east of San Diego. It encompasses an area bisected by the New River, where smugglers are known to guide people through polluted waters. The project, which includes a bridge over the river, is expected to take 300 days.