to go in the desert after you get the go goggles and pick up the claw fossil. then talk to
one of the science guys in the devon building and then you will an anorith with the dig
move

trapinch learns it at level 41 and the little kid at the fossil maniacs house will give
you one (fossil maniacs house on pokenav

The TM itself is found just west of Fallarbor Town.

Just west of the city is a the "Fossil Maniac's House." Go inside and enter the cave
entrance on the back of the wall. At the end of the cave, you'll see the Fossil Maniac;
talk to him, and he'll give you the TM to make you go away.