A report from lifeguards in Del Mar warned the North County Transit District about a cliff collapse along the tracks just before 10 a.m. Monday.
Train service was temporarily halted between Solana Beach and Sorrento Valley while NCTD and lifeguards investigated.
The area of the cliff failure was described as between 9th and 10th streets in Del Mar.
A view from Skyranger 7 shows a slide on the west side of the bluff, approximately 10 to 20 feet from the tracks.
An inspector arrived and decided to run a train through the area at a slow speed.
The route was reopened within the hour.