Classic McCormick Loop Monday

10.3 Ks ,  half Snowmobile/Tractor Trail and half road today.  I was able to move along well on the snowmobile trail punching through a few centimeters of slushy snow but when I hit the not traveled tractor trails I really slowed down .  When it gets tough you can see where the cadence drops ,  the pace slows ,  the vertical osc drops,  ground contact increases  and my HR climbs!    Spike the HR running a hill that doesn't really stand out on the elevation profile ... topo maps of the area are good but small features are missed.