I got to do a quick POTA actviation of Fishlake National Forest last night. Mapping out the calls revealed things about the landscape. Looking at the QSOs map tonight, I immediately saw a limiting case. The QSOs to Oregon and Louisiana make almost a straight line. Zooming in on them shows 'wall' defined by that line.Rotating the heading of the map though, shows the hill right behind the antenna site. The radio waves in that direction went straight into the hill. References: Fishlake National Forest K-4396