You were advised by previous reports that the advance of the enemy made its appearance in the neighborhood of this post as early as the 12th ultimo. His force consisted of Riley's and Green's regiments, five companies of Steele's and five of Baylor's regiments, Teel's and Ripley's batteries, and three independent companies, making a nominal aggregate, as indicated by captured rolls and returns, of nearly 3,000 men, but reduced, it was understood, by sickness and detachments to about 2,600 when it reached this neighborhood.
To oppose this force i had concentrated at this post five companies of the Fifth, three of the Seventh, and three of the Tenth Infantry, two companies of the First and five of the Third Cavalry, McRae's battery (G of the Second and I of the Third Cavalry), and a company of Colorado volunteers. The New Mexican troops consisted of the First Regiment (Carson's), seven companies of the Second, seven of the Third, one of the Fourth, two of the Fifth, Graydon's Spy Company, and about 1,000 hastily-collected and unorganized militia, making on the morning of the 21st an aggregate present of 3,810.
Having no confidence in the militia and but little in the volunteers, I had determined from the first to bring on a battle if possible in a position where the New Mexican troops would not be obliged to maneuver in the presence of or under the fire of the enemy. Several days were spent in the endeavor to accomplish this object, which failed, for the reason that several officers of the Confederate force had lived or served in New Mexico and thoroughly understood and appreciated the character of its people.
On the 19th the enemy fell back from his advanced position and crossed to the east bank fo the river, about 7 miles below the post, with the evident intention of reaching the country above without fighting or of forcing us to attack him upon ground of his own choice. On the 20th the first movement for tuning the post or occupying a point within range which commanded it was commenced, and in order that the operations of this and the subsequent day may be understood it is necessary to give a short topographical sketch of the country embraced in these operations.
From Paraje, 7 miles below, to a point immediately opposite the post, the valley of the Rio Grande is bounded on the east by a basaltic mesa from 40 to 80 feet in height, accessible at a few points by bridle-paths, and at only one point by a road practicable for artillery. Immediately opposite the spot a point of the pedregal projects into the valley, and at the distance of 1,000 yards has a slight command over the post, which would be tenable only by preventing the establishment of batteries on the point. Two and a half miles above the post the Mesa del Contadero, about 3 miles long and 2 wide, rises to the height of 300 feet above the level of the valley. At the southern and northern ends of this mesa the valley of the river is accessible, and at both points was favorable for the establishment of a camp beyond the reach of our artillery and covered in front by the river itself.
The mal pais, or pedregal, is traversed by ridges of drifting sand, broken in places by protruding beds of lava, and parallel in their general direction to the valley of the river. The ravines between these ridges are natural covered ways, affording the enemy great advantages, by concealing his movements and securing him from attack by the impracticable character of the country between them and our position.
On the 20th the main force of the enemy moved up one of these ravines, and at 4 o'clock in the afternoon had reached a position in which it was possible to attack him, although the ground in his front