start of herbert brook trail

ok- i have not done this trail in awhile- where does the trail actually start? co ming in from UW i walk across the flowed lands to the end staying on left side to that lean to in the corner- is this mcmartin lean to or herbert brook lean to? where is the actual start of the trail up? i remeber a tiny little bridge? any one actualy have a hand drawn map of the route and turns? thanks