The run begins just underneath the Long Trail footbridge. Here the wide cobble-laden Mill River funnels between bedrock walls as it drops into the upper gorge. While you can easily put in on either side, it is more fun to bounce across the suspension bridge to put in on river left just upstream.
The first gorge contains approximately a half dozen rapids. For the most part these are boat-scoutable by a confident group, otherwise you can see the majority of this gorge from the left bank before setting out. If the rapids directly under the bridge don’t look like your cup of tea it is best to not put on.