Spray a 9x13 pan with cooking spray & set aside

Pop your popcorn & pour into a large bowl

In a medium saucepan combine marshmallows & butter

Heat over med-low until completely smooth- stirring constantly

Remove from heat & pour over prepared popcorn

Fold until all popcorn is coated with marshmallow

Add trail mix & continue folding until mixed in

Transfer to prepared dish & spread out into an even layer

Allow to set at least 10 minutes before cutting into bars