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Gutierrezia elegans

MANCOS SHALE

    The following photographs show the first two Mancos Shale sites on which Gutierrezia elegans was found.  The Shale of the first site (shown in the first four photographs) is far less eroded than the shale of the second site (the last photograph).  The first site has numerous small shale rocks and the soil is quite dense, making it more difficult for vegetation to grow.  On the second site the Mancos Shale is far more weathered and the surface has at least 3-4 times the vegetation cover that the first site has.

    In the photos of the first collection site notice not only the sparseness of the vegetation but also that the vegetation tends to grow in straight lines above the sub-surface fractured, thin layer of limestone. The first two photos show the surface, the third shows a slope into a water-course eroded area of bare rock, and the fourth, 200 feet farther down that water-course, shows a cross section of the Mancos Shale exposed as the periodic rains and snow-melt cut deeper into the sub-surface.

    As barren as the first site appears, it really has an abundance of plants, many unusual.  In addition to the endemic Gutierrezia elegans, one other shale endemic, Physaria pulvinata, was recently discovered. Gutierrezia elegans was discovered in the Park; Physaria pulvinata was discovered north of the Park and later also found abundantly in the Park.

    In addition to finding these two rare plants, we have found at least two dozen other plants not previously found in Dolores County ("county records").  Something about the Mancos Shale is providing conditions just right for these plants to grow, and perhaps these same conditions are inhibiting the growth of more common plants found nearby. We have taken soil samples and hope in the near future to chemically analyze the plants themselves to see if that helps us understand what is producing such fertile ground for so many unusual plants. 

    One theory is that it may not be any chemical composition of the Mancos Shale that is fostering the growth of these plants, but instead it may be the physical characteristics of the Shale that inhibit the growth of some plants and allow the growth of others.  Seeds of these newly discovered plants and the other unusual plants are obviously finding the Shale a very suitable place to mature.  The soils drain quickly but after a rain hold water at the surface.  The sub-surface limestone cracks may be another factor favoring the growth of some plants and retarding the growth of others.

Gutierrezia elegans first collection site
The first site where Gutierrezia elegans was discovered has numerous small shale rocks and very find shale that makes the soil dense, perhaps making it more difficult for some vegetation to grow. The yellow flowering plants in the lower half of the photograph are Gutierrezia elegans.  
Plants growing in straight lines in Mancos Shale at first collection site
Vegetation tends to grow in straight lines above the sub-surface limestone cracks.
Cracks in limestone which underlies the Mancos Shale
This photograph shows a more solid limestone which has been exposed by erosion of the Mancos Shale.  Notice the pronounced cracks that give rise to the straight lines of vegetation shown in the above photograph.
Cross section of Mancos Cracks at first collection site
This is a cross section of the Mancos Shale about 200 feet farther down the eroded water-course from the above photograph. 
Gutierrezia elegans second collection site
On the second site that Gutierrezia elegans was found on, the Mancos Shale is far more weathered and the surface has at least 3-4 times the vegetation cover that the first site has.