Yup! All rail traffic between Los Angeles and San Diego runs through Del Mar. The bluffs often crumble and collapse onto the beach below. And each time it happens, they have to close that portion of the Surf Line to carry out thorough inspections to make sure it's not going to bring a train down with it. It's been an issue as far back as the steam age. December 31, 1940, a northbound Santa Fe freight tumbled down after heavy rains destabilized a section of the cliffs. They've been shoring them up with heavy retaining walls for years now, but moving the tracks inland is the eventual goal. But that $300 million will only cover a fraction of how much a tunnel under the city will cost. [old pic of Coaster train riding along the bluffs]
It's a shame though, that portion of the Surf Line is one of the most scenic on the route. Makes the morning commute on the Coaster quite special. But as can be seen in this pic, the rail line through Del Mar is sandwiched between the bluff edge and residential areas, so no double-tracking can be done there.
San Clemente (a few dozen miles north of Del Mar) is having a similar issue. With rising sea levels, the waves are coming right up to the tracks at high tide. No hope for double-tracking there. The Surf Line may have to be moved inland in this area, as well. [pic of Surfliner at San Clemente]