I would direct you to the maps in the Cimarex and Newfield presentations that they post of their websites. The southeastern part of Blaine is quite active right now.
"Harder" rock is usually "Tighter" rock and has less porosity (holes) and permeability (connectors between the holes-think of a bar bell). Gas molecules are smaller than oil molecules, so can get through the smaller pores and pathways. Harder rock is also tougher on drilling bits, so it takes more time to drill through it.