Rockhounding Contra Costa County, California: 9 Places To Hunt Rocks, Crystals, and Fossils  

If you are looking for a great place to go rockhounding, look no further than Contra Costa County in California.

This county is home to a variety of rocks, minerals, and crystals that make for great finds.

Here are 9 of the best places to go rockhounding in Contra Costa County.

Rockhounding Contra Costa County, California


The information provided in this article by is for informational purposes and is subject to change. Laws are updated. Accessibility guidelines and restrictions change. Be sure to confirm the land status and collection rules before you travel to an unfamiliar location or collect any material.

Mt. Diablo State Park

Mt. Diablo State Park is an incredibly popular location for rockhounding, as there is ample opportunity to find a variety of rocks and minerals like quartz, calcite, and Tuolumne.

There are numerous hiking trails available for rockhounds to explore for gems and landmarks like the Rock City formation for visitors to enjoy.

There is a $10 fee to enter and park at this location, though you must leave by sunset to avoid having your vehicle locked behind the gates.

Certain areas of the park are closed periodically throughout the year for falcon nesting, so be sure to check for conditions on the official website before leaving on your trip.

Black Diamond Mines Regional Preserve

The Black Diamond Mines Regional Preserve is another great spot for rockhounding in Contra Costa County.

The preserve boasts over 6,000 acres of landscape to explore for rocks, as well as an incredible array of well-maintained trails to hike and search.

The Ridge Trail, Coal Canyon, and Black Diamond are some of the most popular trails that rockhounds search for gems like quartzite and moonstone.

There is a $5 fee to park and enter the preserve, though the hours can vary depending on the season and weather conditions.

To find the main entrance, travel on Highway 4 to the Somersville Road exit in Antioch.

After taking the exit, drive south until you reach the park entrance.

Tilden Regional Park

If you are looking for a rockhounding location with breathtaking views and family-friendly facilities, Tilden Regional Park is one spot you won’t want to miss.

Like many of the other locations, jasper, agates, and quartz are some of the most popular items found in the park, especially along the Vollmer Peak Trail.

There is no fee to park or enter this location, with the standard opening hours falling between 5 AM and 10 PM.

If you are rockhounding with kids, be sure to stop and check out the train and merry-go-round in the park.

Briones Regional Park

Briones Regional Park is another popular rockhounding location in Contra Costa County that is nestled in the Briones Hills.

The park has over 6,000 acres of beautiful land to explore for rocks, gems, minerals, and fossils, along with breathtaking flowers during some seasons.

While this location is suitable for most experience levels, be sure to note the steep elevation on the Abrigo Valley Trail, Mott Peak Trail, and Black Oak Trail.

There is a $3 fee to park and enter the park, though this is only in effect during some business hours.

Be sure to check the official website for conditions and updates regarding operating hours.

Castle Rock State Park

Castle Rock State Park is a rockhound’s dream, as this landscape is covered in stunning sandstone and dense forests.

The park has over 30 miles of trail systems to explore the lush land for plant fossils and an incredible array of rocks.

The park’s trail system links the Santa Clara and San Lorenzo valleys, making this a perfect central location for nearly any type of rockhounding trip.

There is a $10 fee to park at this location, though it’s important to note there is no cellphone service anywhere in the park.

Be sure to bring enough supplies for your trip if you plan to visit.

Sanborn County Park

Located in the Santa Cruz Mountains, the Sanborn County Park is an incredible location for rockhounding the 3,453 acres of landscape.

Many rockhounds search along the redwoods and various trailheads to find some of the most incredible geologic material in the area.

The park is open from 8 AM to sunset daily, though there is a fee to park your vehicle.

If you choose to camp at this location, additional fees will be collected.

Be sure to note that the gate closes at sunset, meaning your vehicle may be locked in if you do not arrive in time.

Mt. Hamilton

If you want a rockhounding location that has hiking, bicycling, and camping, this is one spot you should check out.

While this location offers some of the most beautiful views in the area, it’s important to stay alert when driving on the dangerous, windy roads.

Parking spaces are limited and timed in this area, so try and plan your visit accordingly.

Due to the unpredictable weather conditions, be sure to wear layered clothing and bring ample amounts of water for your trip.

Mt. Tamalpais

Often referred to as “Mount Tam,” Mt. Tamalpais is a popular location for rockhounding, hiking, horseback riding, and hang-gliding.

Visitors can hike the different trail systems at the mountain to search for their rocks, or they can drive to the top of the mountain and search while enjoying the views.

The hike is considered acceptable for all experience levels, though the elevation does reach 2,571 feet.

There is no fee if you park at the state park entrance, but the gates will close at sunset.

However, there are parking fees at the East Peak, Pantoll, and Bootjack trailheads.

Folsom Lake

Located just 25 miles from Sacramento, Folsom Lake is an incredible location for rockhounding and finding valuable gems and minerals.

The Johnny Cash Trail and the Folsom Lake Trail are the two most popular systems for rockhounding, as there are multiple spots to stop and search the water’s edge for rockhound treasure.

There is a $12 fee to park at this location, though this price can change depending on where you park or what entrance you utilize.

Now that you know of 9 great spots for rockhounding in Contra Costa County, California, get out there and start hunting for rocks, minerals, and fossils!

Remember to follow all regulations and guidelines set forth by the parks and recreation areas, and have fun!

California Rockhounding Resources

If you like to have a physical book in hand (like when there’s no cell service), here’s a few popular options:

Rockhounding California: A Guide To The State’s Best Rockhounding Sites

Gem Trails of Southern California

Gem Trails of Northern California

Smithsonian Rocks and Minerals Identification Guide

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Rockhounding Contra Costa County