These small ceramic pieces on the ground are called pot sherds.  They are remains of a broken pot, probably fired by the Hohokam people.  These pieces have no designs on them, possibly indicating that they made up a utilitarian pot or dish. 

It is very important that you leave all archeological materials where you see them.  Don't move them. People who take these remains not only commit a formal crime, they steal from us all by preventing archeologists from piecing together what happened in the past.