A towhead is a sandbar that has cottonwoods on it as thick as harrow-teeth.

沙一片沙土岗子，上面长满了白杨，密象耙齿一般。

As soon as I got started I took out after the raft, hot and heavy, right down the towhead.

船一开动，我就顺沙，木筏，拼命追去。