The incident occurred about 9:45 a.m. at an enclosed federal work zone in Otay Mesa. The man was able to slow his fall by extending his elbows in the large shaft, which was being excavated for a concrete footage. He was apparently uninjured when he emerged from the hole and immediately returned to work.
Members of the news media were on a tour of the construction site at the time of the accident.
Construction of eight border-wall prototypes had begun Tuesday at the location. They are expected to be completed in about 30 days.