Grandview Beach can be reached by wooden stairs from a parking lot above.
A slab of the cliff that was approximately 10 metres long collapsed on a number of people that were relaxing on Grandview Beach, which is north of San Diego.
A total of five people were injured when the bluff toppled onto a beach filled with people trying to escape the heat, fire officials said.
Video footage shows beach chairs and umbrellas strewn around the fallen rock, as firefighters and rescuers survey the damage.
"We are devastated by the tragedy today and our hearts go out to the victims and their families", Encinitas Mayor Catherine Blakespear said in a statement.
"I saw first responders, and I saw lifeguards frantically digging people out of the debris", Pepperdine said.
A fourth person remains in hospital, while a fifth suffered minor injuries.
One person was found dead at the beach, while two others who were transported to a local hospital in critical condition were later pronounced dead, according to city officials. The failure isn't affecting structures at the top of the cliffs, he said. Beachgoers are warned daily by lifeguards to stay clear of the area in case of such collapses, officials said.
Search dogs were brought in to hunt for other possible victims, and a skip loader was used to move the dense, heavy debris. Many bluffs are fortified to prevent multimillion-dollar homes from falling into the sea.
Suburbs north of San Diego have long contended with rising water levels in the Pacific Ocean that pressure bluffs along the coast. It is fairly narrow, with tides high this week. Surfers often lay their boards upright against the bluff. People lounging on beach chairs or blankets are sometimes surprised as waves roll past them and within a few feet of the walls.
At a news conference, Encinitas Lifeguard Capt. Larry Giles said his agency will post a lifeguard in the area and keep an eye on the site. Numerous beaches in the area are marked with signs warning of the danger of unforeseen slides.
"It's sandstone that sits on other soils, and then sandstone again", said Brian Ketterer, an official with California State Parks. "There's really no rhyme or reason", Giles said of the collapse.
The immediate area adjacent to the collapsed bluff will remain closed to the public until further notice, the city announced on its website.