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Limestone in Paso Robles

Yesterday, I was over for a Paso Robles Rhone Rangers meeting at Halter Ranch.  Halter is a beautiful property just across Adelaida Road from Tablas Creek, and both were parts of the old Macgillivray Ranch through most of the 20th century.  After our meeting, Ranch Manager Mitch Wyss took me down to a little waterfall in Las Tablas Creek just behind their ranch buildings.  Although Las Tablas Creek is dry (or just trickling) for most of the year, in the spring there's enough water to splash merrily down the waterfall.


I was struck by how dramatically the waterfall-driven erosion had exposed the limestone layers that underlie this Adelaida area.  According to the prevailing view, the bulk of the calcareous clay that we have out in this neck of the woods isn't true limestone, although it shares much of the chemical composition.  And, this is a good thing, as limestone is hard, too hard for vines' roots to break up or break through.  However, there are bands of true limestone that run throughout the region, and the waterfall illustrated one place where the water had broken through a 9-inch limestone layer and was eating its way through the softer clay layers underneath.  Another view, this time from inside the riverbed, with some drying layers of the calcareous clay in the foreground:


The sides of the little canyon were a great illustration of the layers we're planting in, with the cap of limestone at the top:

Limestone_layers Limestone_layers_profile_with_trees

As further evidence of where the roots need to get to to find nutrients, there was a big old oak tree root that had pushed through the limestone and was snaking its way horizontally below it:


And finally, one more photo, a closeup of where the root emerges from the eroded hillside:


Finally, back at Tablas Creek (where we don't have intact limestone layers like at Halter) one photo of what we do with all the broken-up pieces of limestone that we've ripped from the topsoil to keep from destroying our tractors: