State officials yesterday discovered an estimated ton of slate rocks illegally dumped near the trail that leads to Makapu'u Lighthouse and were looking for possible witnesses to the incident.

Kai'wi Park caretaker Kevin Mashima said he suspects that a private construction company disposed of the rocks in the trail parking lot Thursday night before the gates closed at 10:30 p.m.

The city requires all concrete and rock debris to be dropped off at a designated dump site in Nanakuli, he said.

The rocks are not preventing visitors from parking in the lot or hiking the trail. This is the first time debris has been dumped at the park.

"The park is convenient for dumping because there are no lights at night, so anyone can easily drive in," Mashima said. Unlike most state parks, Ka'iwi Park remains open after 7:45 p.m.

"We're trying to see if anyone from the public saw a dump truck last night," he said.

Ka'iwi Park opened in April 2006 after the state built two parking lots — one near the ocean lookout and another at the start of the paved two-mile walking trail that leads to the Makapu'u Lighthouse.