Del Norte County Manzanitas

A subduction event.

One of the most interesting geologic stories in western North America is told by the ultramafic  rocks that were formed deep in the ocean floor. As the Pacific Plate collided and dove beneath (subduction) the North American Plate, the bottom layers from deep oceanic mantle were scraped (obduction) onto the North American Plate. These depositions are referred to as ophiolites and the Klamath Mountains present some of the most extensive examples on Earth.

Serpentines of the High Divide with Jeffrey Pine and Knight's Pinemat Manzanita -- by John O. Sawyer.

Serpentines of the High Divide with Jeffrey Pine and Knight’s Pinemat Manzanita in the foreground– by John O. Sawyer.

The obducted ophiolites consist of a suite of layers. From the bottom to the top, ultramafic rocks like peridotite are beneath gabbro, followed by sheeted basalt dikes, pillow basalts, and then other sedimentary rocks. The icing on the cake is loosely deposited sediments from oceanic organisms. Each of these layers of igneous rocks (excluding the top layers of sediments) become progressively laden with minerals containing high concentrations of metals like iron and magnesium. The deepest layer, the ultramafics, contain the highest concentrations of minerals.

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Sunrise along the High Divide in Del Norte Country — a botanical and geological wonderland.

The concentrated minerals in serpentine constrain some plants from performing various metabolic functions; for example, high levels of magnesium restrict a plant’s uptake of calcium. Plants that can survive on these soils are slow-growing. Many of these plants have become geographically and reproductively isolated from parent populations and in some cases have evolved into new species. Sawyer (2006) has recorded 200 endemic plants on the serpentine outcrops of northwestern California. Three of these are manzanitas!

four-species

Sample treatments from Field Guide to Manzanitas. This includes four of the nine species that can be found in Del Norte County, California–including two endemics.

Arctostaphylos species in Del Norte County (*endemic or near endemic)

  • canescens subsp. canescens
  • columbiana
  • glandulosa subsp. glandulosa 
  • glandulosa subsp. cushingiana
  • hispidula*
  • nevadensis subsp. nevadensis
  • nevadensis subsp. knightii*
  • nortensis*
  • patula
  • uva-ursi
  • viscida subsp. pulchella
A hike along the Bigfoot Trail near Redwood National Park offered 5 manzanita and 8 conifer species.

A hike along the Bigfoot Trail near Redwood National Park offered 5 manzanita and 8 conifer species.

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The effects from the 2015 Coon Fire can be seen  along the South Fork of the Smith River.

norcal-destinations

More reasons to explore: Featured destinations in Northwest California to find manzanitas from Field Guide to Manzanitas.

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