Elephants are sympathetic animals that have been known to help each other when they are distressed. They also show something resembling grief when one of their own dies.
The discovery on Saturday was prompted by a report of several elephants on a nearby road, Thai officials said.
The Haew Narok Waterfall was closed to visitors after the dead elephants were discovered. It was also the site of a similar incident in 1992, when eight elephants fell to their deaths there, BBC reported.
Khao Yai is Thailand's third-largest national park. Haew Narok, the park's tallest waterfall, has three tiers that total about 149m. Elephants are common nearby.