Why do Ponderosa Pines not like Opeche Shale as a soil to grow on?

Answer 1

It is likely too salty.

The Opeche Shale in North Dakota is characterized by bedded evaporites and siliciclastics (clay, sandstone). The evaporite beds are the salt (halite, gypsum, anhydrite) left over as ancient playas dried up.
http://jsedres.sepmonline.org/cgi/content/abstract/70/1/159
pubs.usgs.gov/ha/ha743/ha743Sheet3.pdf - Supplemental Result

The ponderosa pines of the Black Hills like to grow on limestone cliffs, clay soil, and red standstone.ubs.usgs.gov/sir/2005/5160/PDF/sir2005-5160part7.pdf - Supplemental Result -