Excerpts from Jim Conrad's
from the March 10, 2007 Newsletter issued from Sierra Gorda Biosphere Reserve, QUERÉTARO, MÉXICO
SUBTERRANEAN DRAINAGE EXPOSED AT RÍO ESCANELA
Thursday Margarita took me up to the ecotour destination of Río Escanela to help brainstorm on improving a trail. The main attraction was a broad, natural rock-bridge spanning the river, with abundant water draining down through the bridge. You can see a shot taken from beneath the very drippy bridge below:
I've used Photoshop on the above image to highlight formations beneath the bridge. Originally the interior showed up as completely black.
One transfixing feature beneath the bridge was something like a downspout from which water gushed abundantly. You can see a much-retouched image of the outgushing, a stream four or five feet broad, shown below:
Another downspout only trickling water during this middle of the dry season, prettily rusty-stained with iron oxide and about four feet from rim to rim, is below:
Río Escanela is a good place for the geologically inclined. Not only are there karst features like the ones shown above, but also at the beginning of the trail you pass by a functioning silver mine. This silver is associated with upwelling magma resulting from the Cocos Tectonic Plate grinding beneath the North America Plate along the Pacific Coast. More on that some other time...
The Río Escanela itself courses through a very deep, steep-walled valley where you can spend all day just looking at exposed rock in roadcuts.