Keep cool at Black Diamond Mines

If the summer heat is starting to get to you, relief might be just a short drive away at Black Diamond Mines Regional Preserve in Antioch. There, inside the Hazel-Atlas Mine, the temperature hovers around 57 degrees all year round. In fact, naturalists even suggest bringing a coat.

The 1920s-era silica sand mine is usually closed to the public, but in July through November it’s open weekends for guided tours. Participants can learn about the history, geology, and mining methods used at the historic Black Diamond Mines. In its heyday, until it closed in the late 1940s, the Hazel-Atlas Mine and other mines within the park produced more than 1.8 million tons of sand used for making glass. Much of it was used by the Hazel-Atlas Glass Company in Oakland.

Visitors can explore 950 feet into the preserved mining tunnel, getting a first-hand glimpse at the geological foundations of the Mt. Diablo foothills. We all know earthquake faults criss-cross the East Bay, but seeing a fault from below ground is an eye-opener.

Ninety-minute guided tours are offered twice a day on July 5, 12, 18, 19, 25 and 26. Participants must be age 7 or older. The cost is $5. To register, go to

On July 11, Black Diamond Mines is hosting an open house. The public can drop by for self-guided tours. The open house is from noon to 4:30 p.m.


If you’re one of those people who loves the summer heat, the East Bay Regional Park District has a few excellent options for you. An informal survey among District staff last week revealed that the absolute hottest place in the East Bay is not Antioch. Not Livermore. But Round Valley Regional Preserve on the eastern flank of Mt. Diablo, where daytime temperatures stay above 100 for long stretches of the summer.

The 1,911-acre park is a gorgeous expanse of grasslands and oaks, with plenty of desert plants such as black sage and chaparral. It’s also home to some animals most often associated with deserts and the Central Valley, such as desert cottontails, the San Joaquin pocket mouse and the endangered San Joaquin kit fox. The Park District is participating in the ongoing Alameda-Contra Costa Biodiversity Study to learn how we can best protect the kit fox and other animals.

The Round Valley staging area is on Marsh Creek Road south of Brentwood and east of Walnut Creek. Dogs are not allowed at Round Valley because of the sensitive habitat.

Other extra-scorching parks nearby include Vasco Caves, Morgan Territory and Brushy Peak.


As the drought continues, water quality remains an issue at some of the Park District’s lakes and shorelines. Warmer-than-normal temperatures and limited rain have created perfect algae conditions at several of our lakes.

Last week, the District closed Lake Temescal for swimming due to a bloom of toxic blue-green algae. The algae can cause skin rashes, gastro-intestinal ailments or other symptoms which can range from mild to severe. It’s especially dangerous for dogs. At least three dogs in the East Bay have died within the past few months after being in contact with toxic algae.

While not all dogs will be affected by swimming or drinking algae-tainted water, the District is advising dog owners to keep their pets out of cattle ponds, creeks and lakes until the algae blooms have cleared.

Elsewhere in the District, Quarry Lakes Regional Recreation Area in Fremont is closed for swimming due to toxic algae. Shinn Pond, also in Fremont, and Lake Chabot in Castro Valley contain toxic algae and are closed for swimming. All the parks remain open for picnicking, hiking and other activities.

Algae blooms are a natural phenomenon and are occurring at lakes and other water bodies throughout the United States. The District tests its lakes at least weekly and will post advisories or close a lake when appropriate. Check for updates and more information.

Speaking of water quality, here’s a chance to learn more about how water is tested. Every Saturday and Sunday, at 9 a.m. at Big Break Visitor Center in Oakley, visitors can use state-of-the-art instruments to test water in the Delta for dissolved oxygen, pH, conductivity and more.

The results go into a regional database that’s used by researchers, scientists and water managers.

The program is free and no registration is required. Big Break Regional Shoreline is located at 69 Big Break Road.


Looking for a place to take train-obsessed kids? Or maybe some train-obsessed adults? The steam trains at Tilden Regional Park continue to delight park visitors of all ages.

The scaled-down Redwood Valley Railway travels through a shady redwood grove and scenic ridge in the wooded hills above Berkeley. With several picnic sites nearby, the area is a great place for a birthday party or afternoon outing.

Horse-drawn train rides are also available at Ardenwood in Fremont. The historic trains are maintained by volunteers from the Society for the Preservation of Carter Railroad Resources, who act as brakemen and drivers as the drafthorse-led train traverses 1 ½-mile of track across the farm.

For information, go to