When it comes to the knowledge of a county engineer that a trespass has been committed on any canal lands or on any lands appropriated by congress for the support of schools or for ministerial purposes of this state, he shall immediately ascertain the extent of such trespass, the names of the trespassers and of witnesses to such trespass, and report them to the prosecuting attorney. For such services the engineer shall be paid such compensation as the court allows from fines collected for such trespass and from the proceeds of sales of timber seized by the prosecuting attorney.