Death Valley geology field tripHarmony Borax Works |
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Tracing the source of Death Valley's borax
The primary source of borate minerals gathered from Death Valley's playas is the 6-4 million year old Furnace Creek Formation. The Furnace Creek Formation forms the remarkably rounded, yellow, brown, and green foothills that are beautifully exposed around Zabriskie Point. The Formation is made up of over 5000 feet of mudstone, siltstone, and conglomerate. Most of the silty mudstones were originally deposited in lakebeds that predate the modern Death Valley basin. The borates were concentrated in these lakebeds from hot spring waters and altered rhyolite from nearby volcanic fields.
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The thick stack of sedimentary layers was then buried and partially hardened (lithified) to form the soft Furnace Creek Formation rocks. These rocks were uplifted and exposed at the surface during the intense tectonic activity that created modern Death Valley beginning about three million years ago.
Water percolating through the ancient Furnace Creek Formation lakebeds dissolved some of the soluble borate minerals and carried them down Furnace Creek Wash to the playa below. As the mineral-rich water evaporated, borate minerals precipitated out of the solution, forming cottonballs on the playa surface.
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