That thin black mat is identical in looks to what I see on the sides of many of the older roads here in Missouri, where they cut into the sides of hills.
I have a feeling that this ‘mat’ is likely predominant across the entire northern continent of America.
Just look at the artificial cliffs where hillsides have been cut along the roads you travel, and I bet you’ll see them as well.
Thanks for the info. I’m sure that there’s traces of this in California, where I am. This will be pretty awe-inspiring if/when somebody maps it.