The Friends of the North Leverett Sawmill will host a free, public event on June 21 to celebrate the official opening of its new heritage park and nature trail. The event will be held at the corner of North Leverett Road and Cave Hill Road from 1-4 p.m. with remarks scheduled for 2 p.m. Visitors will be able to enjoy the park’s new riverside pavilion, observe native flora and fauna along its nature trail, investigate nearby industrial ruins, and tour the historic sawmill building. An art exhibition, showcasing work by more than 40 artists, including Pioneer Valley favorites, will feature the sawmill and environs in a wide variety of media.