WHITE SALMON — David Johnson uses a simple rule of thumb to find solid ground in the ever-shifting landscape around the White Salmon River, snaking through a deep muddy canyon that used to be Northwestern Lake.Look for a tree trunk.“If you don’t see a tree trunk,” Johnson said, “you’re not there yet.”In other words: Many of the soft, bare slopes that now plunge toward the river’s new path — and a handful of tributary creeks feeding into the former reservoir — won’t be there for long.“There’s a lot of dirt up here still to be moved out of here,” Johnson said. “It’s still changing.”The White Salmon began charting its new course Oct. 26, when a blast of dynamite breached Condit Dam and drained Northwestern Lake in barely an hour. Nearly a century’s worth of mud and sediment buildup behind the dam started working its way down toward the White Salmon’s confluence with the Columbia River.Much of that process will depend on how much rain and snowmelt the coming months bring. But as it starts to play out, a few cabin owners along the former reservoir fear they might lose more than a lakefront view. Erosion continues to rapidly reshape the landscape, in some places washing away banks uncomfortably close to structures and docks. Those impacts are evident even past Northwestern Park, about a mile and a half upstream of Condit Dam.PacifiCorp, which owns Condit Dam and the surrounding land that dozens of cabins sit on, has constantly monitored conditions since the day of the breaching. Contractors JR Merit and Kleinfelder occupy a sort of home-base office in a building just a stone’s throw from the dam itself.