A person on a dirt bike is riding up a sandy hill.
A person rides a bike on the dunes at the beach.
Just because the person is riding up a sandy hill does not mean that the sand is at the beach, the sandy hill could be in a desert or some other location.
exists e1 s1 x1 x2 x3 x4 x5.(a_up(s1) & Manner(e1,s1) & Theme(e1,x4) & Actor(e1,x1) & v_ride(e1) & n_hill(x4) & of(x4,x5) & n_sandy(x5) & on(x1,x2) & n_bike(x2) & of(x2,x3) & n_dirt(x3) & n_person(x1))
exists e1 x1 x2 x3 x4.(n_beach(x4) & n_dune(x3) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & on(x2,x3) & at(x3,x4) & n_bike(x2) & n_person(x1))