HOUGHTON, Mich. (Michigan News Source) – The Keweenaw Sheriff’s Department released a statement reminding residents and visitors that exploring the old copper mines in the U.P. is illegal.

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The announcement comes after two Houghton County men were recently sentenced.

Brent Hiltunen and Ike Kinsinger, both of Calumet, will spend 30 days in jail after being arrested and sentenced on breaking and entering charges. In addition, officials said they took minerals from the mine.

Authorities specify the dangers to those entering as well as the danger it places on first responders who are called to the scene.