Near Antioch in Contra Costa County, California — The American West (Pacific Coastal)
Greathouse Portal
A Hidden World Awaits
Photographed By Barry Swackhamer, April 1, 2016
1. Greathouse Portal Marker
Captions: (bottom left) Greathouse Portal as it appeared in the late 1970s. In 2012, after being closed for four due to storm damage, work was completed on the new portal allowing visitors access once again.; (bottom center) Miners toiled to remove silica sand, leaving behind nearly eight miles of underground workings.; (bottom right) The sand bunker at Greathouse Portal at the lower most level of Hazel-Atlas Mine as it appeared circa 1948. From the early 1920s to the mid-1940s, silica sand was mined at this site and transported to the Hazel-Atlas Glass Company factory in Oakland, California, where it was used to make glass products.
Inscription.
Greathouse Portal. A Hidden World Awaits. Take a moment and gaze down the Greathouse Portal, your entrance into vast underground spaces filled with an intriguing human and geologic history. What was once the ocean floor provided raw materials (silica sand) for glass making during the early twentieth century. , When R. Marvin Greathouse began hollowing these hills to mine the silica sandstone, he could not have known that the cavernous rooms left behind would fascinate people for decades to come. , Today this portal serves as your gateway to the past and entrance into a unique underground visitor center. Join us during open house, and step into the earth and into the past.
Take a moment and gaze down the Greathouse Portal, your entrance into vast underground spaces filled with an intriguing human and geologic history. What was once the ocean floor provided raw materials (silica sand) for glass making during the early twentieth century.
When R. Marvin Greathouse began hollowing these hills to mine the silica sandstone, he could not have known that the cavernous rooms left behind would fascinate people for decades to come.
Today this portal serves as your gateway to the past and entrance into a unique underground visitor center. Join us during open house, and step into the earth and into the past.
Erected by East Bay Regional Park District.
Topics. This historical marker is listed in this topic list: Industry & Commerce.
Location. 37° 57.297′ N, 121° 51.928′ W. Marker is near Antioch, California, in Contra Costa County. Marker can be reached from Somersville Road. Touch for map. Marker is at or near this postal address: 5175 Somersville Road, Antioch CA 94509, United States of America. Touch for directions.
Other nearby markers. At least 8 other markers are within walking distance of this marker. Mount Diablo Coal Field (within shouting distance of this marker); Eureka Slope (within shouting distance of this marker); Somersville Townsite (approx. 0.2 miles away);
More about this marker. This marker is located at the Greathouse Visitors Center in Black Diamond Regional Park.
Photographed By Barry Swackhamer, April 1, 2016
2. Greathouse Portal and Marker
Marker on the right.
Photographed By Joseph Alvarado, May 7, 2022
3. Shaft connecting Greathouse Portal and Hazel-Atlas Portal
Photographed By Joseph Alvarado, May 7, 2022
4. Greathouse Portal Marker
On the wall inside the mine
Photographed By Joseph Alvarado, May 7, 2022
5. Greathouse Portal Marker
On the rock wall of the visitors center, inside the mine.
Photographed By Joseph Alvarado, May 7, 2022
6. Hazel-Altas Silica Sand Mine
On the rock wall of the visitors center, inside the mine.
Photographed By Joseph Alvarado, May 7, 2022
7. Railcar Port-O-Potty
Photographed By Joseph Alvarado, May 7, 2022
8. Adjoining Hazel-Atlas Mine
Credits. This page was last revised on August 29, 2022. It was originally submitted on April 5, 2016, by Barry Swackhamer of Brentwood, California. This page has been viewed 645 times since then and 127 times this year. Last updated on May 8, 2022, by Joseph Alvarado of Livermore, California. Photos:1, 2. submitted on April 5, 2016, by Barry Swackhamer of Brentwood, California. 3. submitted on August 26, 2022, by Joseph Alvarado of Livermore, California. 4, 5, 6. submitted on May 21, 2022, by Joseph Alvarado of Livermore, California. 7, 8. submitted on August 26, 2022, by Joseph Alvarado of Livermore, California. • Syd Whittle was the editor who published this page.