BLACK DIAMOND Mines Regional Preserve in Antioch will host an open house from noon to 4:30 p.m. Sept. 26 at its Hazel-Atlas Mine underground museum.

Visitors will be able to take free, self-guided tours of the historic mine, with park staff and volunteers posted along the way to provide information and answer questions.

For safety reasons, visitors must be age 7 or older, and children must be accompanied by an adult. Kids younger than 7 are welcome to get the underground feeling by visiting a section of sand mine just inside the portal gate.

About 1,000 feet of old mining tunnels are open to the public, including the mine foreman's underground office and chambers created by sand extraction. Vintage mining equipment also will be on display.

Concurrent with the open house, Black Diamond supervising naturalist Traci Parent and volunteer Karen Terhune will host a book signing and sale in one of the mine chambers. Parent and Terhune have co-authored a book of photos and text bringing back to life the park's 19th century coal-mining era.

It's titled "Arcadia's Images of America: Black Diamond Mines Regional Preserve," and copies will be available for purchase.

Black Diamond will offer 90-minute guided tours of the underground mining museum every weekend through November. Advanced reservation tours take place at 11 a.m., 1 p.m. and 2 p.m.

A 10 a.m. tour is available to groups of 10 or more. First-come, first-served tours are at noon and 3 p.m. Tour cost is $3 per person. For more information, phone the East Bay Regional Park District reservations department at 1-888-327-2757.

If you'd rather stay above ground, naturalist Eddie Willis will offer a program about owls from 2 to 3 p.m. Sept. 27.

The program will be at the park visitor center, located in the cluster of buildings to the left of the entrance kiosk on Somersville Road. Black Diamond Mines has a parking fee of $5 per vehicle when the kiosk is attended.

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Summer does not end officially, at least astronomically, until the autumnal equinox on Tuesday. To bid farewell to the season, Willis will lead an end-of-summer hike from 8 a.m. to noon Sunday at Morgan Territory Regional Preserve east of Mount Diablo.

It's a six-mile trek, with a moderate amount of hill climbing. You'll be rewarded by great views of Mount Diablo and the Delta, as well as glimpses of Morgan Territory's abundant but elusive wildlife.

The hike is free, but reservations are required. Phone 1-888-327-2757. Select option 2, then 3, and refer to program number 22543.

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Bird watchers will enjoy assisting in a research project from 9 to 11:30 a.m. Thursday at Round Valley Regional Preserve south of Brentwood. The group will attempt to spot and count the various raptors that inhabit the park. No experience is necessary; participants will be taught how to identify the birds.

Meet at the Round Valley staging area on Marsh Creek Road. There's no fee, but registration is required. Phone 1-888-327-2757, select option 2, then 3, and refer to program 22544.

Ned MacKay writes a regular column about East Bay Regional Park District sites and activities. E-mail him at nedmackay@comcast.net.