By Velena Jones

TUOLUMNE COUNTY (CBS13) — A report of a loud “explosion” led to the discovery of some cracks in the Twain Harte Lake Dam on Thursday, authorities say.

According to the Tuolumne County Sheriff, first responders went to investigate the noise and discovered some cracks in the dam.

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Officials say there were no signs of explosive devices found. Instead, authorities believe people most likely heard rock at the dam cracking. The sheriff’s office says water was released from the lake due to the situation.

After reviewing the extent of the damage, the Tuolumne Office of Emergency Services said Thursday evening that the evacuation advisory issued during the afternoon was lifted due to the dam appearing to be structurally sound.

“When there is a big boom that everyone heard, you wonder whats going on,” said Kathy Bigham, a resident within the advisory zone.

The advisory impacted areas downstream from the dam including: Good Shepherd Drive, Lucky Strike Trail in Upper Crystal Falls, and all areas east of the Sullivan Creek Bridge along the creek. Dore Bietz, the director of the Office of Emergency Services, said more than 150 structures were under the advisory.

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“You never know what’s going on underneath the Earth,” Bigham said. “Weird things can happen.” 

The issue appears to be similar to an incident that happened at the dam back in 2014. A granite dome right next to the dam fractured in what scientists called an “exfoliating” event. People also reported hearing loud and explosive pops.

The tense situation played out in the small community of Twain Harte, about 10 miles Northeast of Sonora.

“Anytime you have a dam failure, the potential amount of water that could come when folks aren’t aware or prepared for it definitely could be of concern,” Bietz said.

Twain Harte Lake Association will continue with draining water from the lake and monitoring the dam.

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Twain Harte Lake is a private reservoir created by the dam. Back in the summer, it was the site of a sewer spill that prompted a temporary closure of recreation activities at the lake.

Velena Jones