DUBUQUE, Iowa (AP) — A northeast Iowa woman says she's been shaken by her discovery of a sinkhole in her backyard garden.

Terri Dolter told the Dubuque Telegraph Herald (http://bit.ly/2vWv5Jc ) that she found the 3-by-4-foot hole (1 meter square) had suddenly appeared Sunday. She says she can't see its bottom and couldn't hear the impact of a brick she dropped into it.

She thinks the hole is evidence of a mineshaft that she didn't know was on the property, which sits in a suburban development on the northwest side of Dubuque. She hasn't confirmed her suspicions, however.

Dolter says an insurance adjuster will examine the hole soon. She's locked the garden's fence gate for now.

The home was built in 2001.

Dubuque County maintenance superintendent Chad Danielson says mineshafts are common in the area.

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Information from: Telegraph Herald, http://www.thonline.com