The performance artists insists his skill is genuine but some people believe his work could be fake.
Dan has been wowing the crowds in San Francisco Bay since 1994 with his stunning sculptures of different-sized rocks resting on top of each other.
He has since picked up a legion of fans on the internet - his work on YouTube has clocked plenty of hits - and has been asked to create sculptures for galleries and private events.
In fact his gravity-defying work is so amazing that people sometimes refuse to believe he doesn't use glue or some other trickery.
'I had so many negative e-mails from curious sceptics saying that it is computerised art that I got tired of explaining over and over again,' Dan said.
'Please no more questions about glue!'
The artist, who is in his mid-50s, claims he can also balance shoes, glassware and cans.
Explaining how he does it, Dan said: 'I don't picture what the sculpture looks like beforehand, it just forms as I work. It is not difficult to stack two or three rocks upwards.
'Don't worry if you start with large contact points, you can get smaller and smaller as you build your skills.'
Dan said he enjoyed the art because it was 'uniquely beautiful'.
'Based on curiosity alone I could create a piece of beautiful art, unlike any other.'
Andrew Burton, one of Britain's most respected sculptors, said: 'I would just say that this is possible – after all, he would be found out pretty quickly if it were not.'