In Roberts Construction Co. v. Vondriska, 547 P.2d 1171 (Wyo. 1976), the Court rejected a gravel mining company's claim of an irrevocable license to stockpile gravel on property adjoining its mine. Finding no permanent improvements had been made on the licensee's property and no expenditures were made in reliance on the permissive use of the stockpile, the Court concluded the elements of estoppel were not proven. While the gravel mining company provided evidence of certain expenditures made in the course of conducting its operation, the Court stated, "it does not appear that any of these operations were in any way peculiar to or irrevocably required the use of this particular tract. These are expenditures which would have had to be made if the limestone was piled on the quarry tract which as we have pointed out Roberts had the full right to under its lease." (Id. at 1177.) The Court reiterated that the law of irrevocable licenses is founded in principles of estoppel. There is little doubt in our minds that the enforcement of oral licenses against attempted revocation is based on principles of equitable estoppel. Summarizing briefly from 28 Am.Jur.2d Estoppel and Waiver 35, p. 640 et seq. the elements of such estoppel, we find that the person estopped must be guilty of conduct which amounts to false representation, intention that such conduct be acted upon, and have knowledge of the real facts. The party claiming the estoppel must be without knowledge or means of knowledge, rely in good faith upon the conduct or statements of the other party, and either take action or refrain therefrom so as to change his position to his injury or prejudice. Application of the doctrine depends upon the facts of each particular case and "manifestly there can be no equitable estoppel if any essential element thereof is lacking or is not satisfactorily proved." (Id. at 1176.)