There was, however, another and more important phase to the third expedition than that of mere exploration. Frémont before leaving Washington was informed that war with Mexico was possible, and received general unwritten instructions looking to such a contingency. The forecast of trouble proved correct, and the preliminary and extensive disturbances in California interfered most materially with the progress of his surveys. Frémont's explorations westward of the Arkansas River had been through and over Mexican territory. In order to place himself in proper position as a non-invader he proceeded to Monterey, Cal., at the earliest practicable moment and applied to the commanding general, Don José Castro, for permission to extend, in the interests of science and commerce, the geographical survey of the nearest route between the United States and the Pacific Ocean. The request was granted promptly and courteously. Scarcely had Frémont commenced his survey in Northern California than he was peremptorily ordered by General Castro, who later appears to have been acting under orders from the Mexican Government, to quit the department; the message being coupled with an intimation that non-compliance would result in expulsion by an armed force. The message was delivered in such manner and language as incensed Frémont and caused him to peremptorily refuse. Withdrawing a short distance he erected a stockade and awaited expulsion by arms. The Mexican force made several forward movements, but carefully avoided an attack. Frémont finally judged it advisable to quit Mexican territory, as his remaining might be detrimental to the United States. He consequently withdrew slowly toward Oregon, surveying and exploring as he moved northward. On May 7, 1845, Frémont was overtaken in the valley of the upper Sacramento by Lieutenant Archibald H. Gillespie, of the marine corps, who brought from Washington important despatches which were destined to settle the fate of California as a Mexican state. Frémont was informed through Gillespie that war with Mexico had been declared, that the government counted upon him to ascertain and conciliate the disposition of the people of California toward the United States, and especially to conserve American interests by ascertaining and counteracting any scheme looking to the cession of California to Great Britain. Frémont was then surrounded by hostile Klamaths, who killed several of his party and with whom he had several engagements, which resulted in the destruction of the principal village, fishing appliances, etc., of the offending tribe.