In order to trap these spies, a small party should be in ambush ahead of the infantry to stop every soul going that way. The cavalry should then march half a day apart until they get near Tucson, so that if they have spies on the trail they will run and tell half the strength of the command, not waiting to see the other half. If our force is shrewd, and knows the strength of the enemy in advance of them, which they ought, and doubtless will know from the Indians themselves, it would seem that it would be impossible for them to fail in taking Tucson. In case of success, every secession man in that town must be brought to Fort Yuma. The party, besides, must endeavor to catch Colonel Reily, if possible. He has gone down toward Hermosilla with twenty men. The instructions in relation to Brevoort are still in force. There must be no surrender. If the party is obliged to retreat, from falling in with an overwhelming force, they must fall back, fighting inch by inch until they get back.

I am, major, very respectfully, &c.,

BEN. C. CUTLER,

First Lieutenant, First Infty. California Vols., Actg. Asst. Adjt. General

HEADQUARTERS DEPARTMENT OF THE PACIFIC,
San Francisco, March 18, 1862.

Brigadier General L. THOMAS,

Adjutant-General U. S. Army, Washington, D. C.:

GENERAL: On the 14th instant I had the honor to acknowledge (by telegraph) the receipt of your dispatch of the 12th* relieving Major-General McClellan from the command of the military departments, excepting that of the Potomac, and directing that hereafter reports be made direct to the Secretary of War. A company of marines having been landed at the navy-yard, Mare Island, from the U. S. flag-ship Lancaster, the presence there of the thirty soldiers of the Third Artillery, as a guard, was no longer required. The detachment has accordingly been withdrawn to its proper on Alcatraz Island. With the view of placing the city and harbor of San Francisco in the best possible state of defense in case of a foreign war, I have, as you are already advised, coused reconnaissance to be made and sites selected for the erection of field-works. I found that our greatest embarrassment was likely to proceed from the want of heavy guns, and I accordingly addressed a communication to Captain W. H. Gardner, U. S. Navy, commanding the navy-yard at Mare Island, on the subject. My letter to Captain Gardner and his reply are both herewith inclosed. + The eighty-nine guns which are placed at my disposal will materially aid us in making up the armament for the batteries. I propose to use every heavy gun I can command for the defense of this city and harbor. Although there are several points on the Pacific Coast that are exposed to capture by a hostile fleet, yet, in case of a war, San Francisco would first attract the enemy's attention. The loss of San Francisco and harbor involves also the loss of our navy-yard and our military arsenal at Benicia. In fact, it destroys for the time all our commerce on the Pacific. Hence this place should be made impregnable.

Very respectfully, your obedient servant,

G. WRIGHT,

Brigadier-General, U. S. Army, Commanding.

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* See President's war order, Numbers 3, March 11, Vol. V, p. 54.

+ See Wright to Gardner, March 12, p. 921, and Gardner to Wright, March 15, p. 926.

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