In a news release, CBP says the first driver was ordered to undergo a secondary inspection when 20 immigrants were discovered in the cargo area.
Moments later, agents stopped a second box truck and discovered 13 immigrants hidden inside.
Monday night, agents working at the Falfurrias checkpoint were told of a lost and injured immigrant who called 911 for help, according to the release.
CBP says using GPS coordinates from the callers cellphone, officers were able to locate the Guatemalan woman who had been abandoned by smugglers. She was taken to an area hospital for treatment.