_Three_ additional medical officers: _One_ officer of the ordnance department: _One_ officer of the subsistence department. The irregular communication with some of the interior posts, creates a good deal of embarrassment by delaying the department returns. In consequence of this I am unable to furnish a later return than for June. The transport Mary and Adeline, with companies A and F, 2d infantry, reached San Francisco on the 8th ultimo. The detachment of dragoons, on their march to the department with the collector of this district and the Arkansas emigrants, have not yet arrived. During the months of July and August, so far as reports have been received, there were but few desertions, except from the company detailed for the escort of Captain Warner, topographical engineers; thirty-four men, more than half the whole number reported, have deserted from this company. The entire force in the department at this time does not probably exceed six hundred and fifty, (aggregate;) and consequently more than four hundred recruits are now required to fill up these companies to the standard authorized for this department. A detailed report of my reconnoissance in the valleys of the San Joaquin and Sacramento will be forwarded by the next steamer. I have delayed it in order to embody in it information in regard to the country in the neighborhood of the Tula, which I am in the daily expectation of receiving. The want of company officers is very much felt; and I request that authority may be given me to break up the companies whose captains are permanently absent, transferring the officers to other companies, as their services may be needed. I have the honor to be, very respectfully, colonel, your obedient servant, B. RILEY, _Brevet Brigadier-General U.S. Army, commanding_. Lieut. Col. W. G. FREEMAN, _Assistant Adjutant General U.S. Army_, _Headquarters of the Army, New York_. APPENDIX M. In the early part of 1848, Lieut. H. W. Halleck, of the Engineers, was ordered to make a reconnoisance of the coast of Lower California, with reference to the location of works of military defence. In his report to Colonel Mason, after giving a general description of the coast and harbors, and proposing a system of military defence, he submits some remarks upon the commercial and military importance of the peninsula. The whole report is interesting, and furnishes the most correct information upon the subject of the reconnoisance. It will form an interesting conclusion to a work which has been principally devoted to a description and history of Upper California. LA PAZ, _April 12, 1848_.