After the Clocks Fall Back: What's Open at Black Diamond Mines and Contra Loma This Winter

Antioch's two regional parks entered November on different schedules, and they are spending the winter on different footing. Black Diamond Mines Regional Preserve has a dated calendar of tours and naturalist walks running through December. Contra Loma Regional Park has shorter gate hours, a trail closure and a planning process that is gathering ideas for the basin where the Swim Lagoon used to be.

Both parks sit in 94509, a short drive apart off Somersville Road and Lone Tree Way. This winter you go to one for its calendar and to the other to help shape its future.

Two parks, two closing times

The East Bay Regional Park District sets gate hours month by month, and November takes a real bite out of both parks. The schedules differ, and that matters if you're planning a late-afternoon walk.

Contra Loma opens an hour earlier and stays open half an hour later than Black Diamond. Before daylight saving ended, Contra Loma's gates stayed open until 7pm. Now they close at 5:30. Black Diamond closes at 5pm through the end of the year, so if you want a walk after work, Contra Loma gives you a little more time. Both parks charge $5 per vehicle for parking. At Black Diamond, that fee applies when the kiosk is staffed, which is seasonal, on weekends and on some holidays.

Underground, the season stays the same

Most of what Black Diamond offers in winter happens below ground, where the weather doesn't reach. The park's Coal Mine Experience is a 30-minute, self-paced underground walk on Saturdays and Sundays all year. Start times are 10:30am, 11:30am and 1:30pm. The district's November–December guide says the mine stays in the mid-50s all year, so the jacket you'd bring in July works in December too. Participants must be at least 7, guardians have to come along, and hard hats are provided.

Tours require registration, and groups are capped at 15 people, which is why the park strongly recommends booking ahead. The route is about a quarter mile of flat, hard-packed dirt. Tours meet outside the Greathouse Visitor Center. The guide lists an ASL tour on Saturday, Dec. 19.

The Greathouse Visitor Center is free to enter. It sits in a chamber dug out in the mid-1920s and shows how a 20th-century sand mine worked, along with displays on the coal-mining era. It's open Fridays from 10am to 2pm and weekends from 10am to 4pm. To get there, walk about a quarter mile past the upper parking lot on a partly paved, partly gravel trail with some incline. Leashed dogs are welcome in the visitor center but not on the mine tours, so if you bring the dog, someone will have to wait outside with it during a tour.

The mine also has money coming in. The park district's 2026 adopted budget sets aside $130,000 for mine shaft safety repairs at Black Diamond Mines and $200,000 to improve public access to the mine.

Black Diamond's calendar, Thanksgiving through December

Aboveground, the preserve's naturalists have scheduled a set of dated programs. The district's November–December Nature Nearby guide says programs are free and drop-in, meeting in the upper parking lot, unless a listing says otherwise. Some programs carry a registration icon, so check each listing before you go.

1. Saturday and Sunday, Nov. 7–8: Coal Mine Experience tours at 10:30am, 11:30am and 1:30pm, registration required.
2. Sunday, Nov. 22, 9:30–11:30am, All-Star Species of Black Diamond: a 2- to 3-mile hike focused on the plants and animals of the preserve's chaparral, with 400 to 500 feet of elevation gain. Best for ages 8 and up.
3. Friday, Nov. 27, 9–11am, Green Friday Hike: a similar 2- to 3-mile chaparral route the day after Thanksgiving, also best for ages 8 and up. The Greathouse Visitor Center adds a special opening that day from 10am to 2pm.
4. Sunday, Nov. 29, 9–10:30am, Thanksgiving Mindfulness Walk: a 1-mile walk with moderate incline and guided prompts. Best for ages 12 and up. It's listed as drop-in with no registration.
5. Tuesday, Dec. 8, 10–11am, Mini Miners: this month's theme for ages 2 to 5 is "Wild Winter Wear: Animal Adaptations for Winter." Siblings are welcome. It's held outdoors rain or shine, though heavy rain may cancel it.
6. Saturday, Dec. 19: the ASL Coal Mine Experience tour.

Heavy rain may cancel most of the hikes, so check the listing on the morning of the walk.

If you want a stop afterward, the Antioch Herald reported in September that Butter Pecan Bakeshop had set an Oct. 2 grand opening for its Antioch location at 3345 Deer Valley Road. The bakeshop's Antioch location page lists hours of 11am to 9pm Sunday through Thursday and 11am to 10pm Friday and Saturday.

Contra Loma, between a lagoon and whatever comes next

Contra Loma's winter is quieter. Some of that is the season and some of it is what's changed at the park.

According to the park district, the Swim Lagoon gave East County a place to swim for more than 20 years. Its sandy shoreline was designed to feel like a beach, and over time that sand damaged the lagoon's lining and water-treatment systems. The district closed the lagoon in 2022. In 2025 it drained the basin and removed the sand while it weighed what to do with the site.

The rest of the park has kept improving in the meantime. The district lists new fishing docks, a renovated boat launch, expanded paths and green space, new ADA-accessible restrooms and picnic sites, and a reopened Loma Island picnic area. The park covers 775 acres around an 80-acre reservoir that's open for fishing all year.

One closure affects walkers this month. The district's Contra Loma page says the Lake View Trail is closed at the cattle pond because of storm damage, and the notice was updated Nov. 1. If you usually walk the full shoreline loop, you'll need to turn back or reroute at the pond. The park map linked from that notice shows the alternatives.

Public input on the lagoon runs through spring 2027

Planning for the basin is underway now, months before swim season. On Sept. 18, the park district announced a public planning process for swimming and recreation at Contra Loma. It started with a Sept. 22 workshop at the Antioch Community Center, 4703 Lone Tree Way. General manager Max Korten described the goal in the release:

"Whether you swim, fish, hike, or picnic here, we encourage every member of the community to attend a workshop, take the survey, or reach out to our team. Your input will shape the swim and recreation features we bring forward for this park."

According to the release, public engagement runs through spring 2027 and includes more meetings, outreach at community events, surveys and interviews. The project page has a short survey in English and Spanish and a contact address for project staff, [email protected]. The district says the options it develops will account for the cost of building as well as long-term staffing and maintenance. The district says a new swim facility is one of the options it will consider, depending on public input.

Two dates on the Contra Loma calendar bring you to the shoreline while those options take shape:

• Friday, Nov. 27, 9am–noon, Green Friday: a free volunteer morning for all ages at the main parking lot, helping with wildlife habitat and ecosystem care. There's a volunteer sign-up, so register before you show up. Black Diamond's Green Friday Hike starts at 9am the same day, so both parks have programs that Friday morning.
• Saturday, Dec. 26, 8:30–11:30am, Winter Bird Walk: a free drop-in program, no registration required.

For swimming next summer, the district points to two seasonal pools nearby, usually open in summer: the Ambrose Aquatic Center in Bay Point and the Brentwood Family Aquatic Complex. The district says it helps keep Ambrose open seven days a week during peak swim season.

For more on what's happening around town, including the restaurants on G Street and by the bridge, see our Antioch neighborhood page.

The Lucas Group keeps up with Antioch's parks and planning updates because they're part of daily life here, from a Saturday mine tour to how the Contra Loma basin gets used next. If you have questions about life on the south side of town or how these changes fit your plans, get in touch. We're happy to talk it through.