“Bite-Size Bits of Local, National, and Global History”
“Bite-Size Bits of Local, National, and Global History”
Near Antioch in Contra Costa County, California — The American West (Pacific Coastal)

Greenhouse Portal

A Hidden World Awaits

Greenhouse Portal Marker image. Click for full size.
By Barry Swackhamer, April 1, 2016
1. Greenhouse Portal Marker
Captions: (bottom left) Greenhouse 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 Greenhouse 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.  Take a moment and gaze down the Greenhouse 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 Greenhouse 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 4 miles of this marker, measured as the
Greenhouse Portal and Marker image. Click for full size.
By Barry Swackhamer, April 1, 2016
2. Greenhouse Portal and Marker
Marker on the right.
Click or scan to see
this page online
crow flies. Somersville Townsite (approx. 0.2 miles away); Mount Diablo Coal Field (approx. ¼ mile away); Independent Mine (approx. ¼ mile away); Sidney Flat (approx. 1.2 miles away); Black Diamond Way (approx. 3.8 miles away); The Eucalyptus Grove (approx. 3.9 miles away); The Growler Saloon – Goethals Building (approx. 3.9 miles away); The Clayton Post Office (approx. 3.9 miles away). Touch for a list and map of all markers in Antioch.
More about this marker. This marker is located at the Greenhouse Visitors Center in Black Diamond Regional Park.
Credits. This page was last revised on June 16, 2016. It was originally submitted on April 5, 2016, by Barry Swackhamer of Brentwood, California. This page has been viewed 275 times since then and 24 times this year. Photos:   1, 2. submitted on April 5, 2016, by Barry Swackhamer of Brentwood, California.

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Oct. 25, 2021