Are the buses that run from Dujiangyan to Huanglong Ancient Town

You need to go back to Chengdu to take the bus.

You can first take the bus at Dujiangyan Bus Center to Chadianzi Bus Station and the buses are available before 19:00 every day and the interval is about 5 - 10 minutes. Then take the bus at Chadianzi Bus Station to Huanglongxi Ancient Town; the buses are available before 18:10.

From Huanglongxi Ancient Town to Chengdu, you can take the bus at the ancient town to Chadianzi Bus Station. The buses are running from 06:50 to 18:00 every day.