WINONA (AP) - At least 35 people have been arrested in Winona during a protest of frack sand mining.

Those arrested were part of a larger group of about 100 and tried to stop sand from being loaded onto barges at the city's harbor. They stood in front of sand trucks for more than an hour, preventing them from moving.

Police Chief Paul Bostrack said that those arrested have been cited for trespassing on CD Corp. property. Catholic Worker Movement spokeswoman Molly Greening says they planned to shut down the frack sand operations. A second simultaneous protest was held at the sand washing facility along Highway 14.

Frack sand is used by oil and gas drilling companies. Opponents of frack sand mining have raised environmental concerns.