Because of a dense fog the delay in reaching the position in rear of the Mexican works was no material disadvantage. The fog began to disappear about the time I reported to General Smith. He was then on a ridge at a point, about 600 yards in rear of the Mexican works. The three brigades were passing around the extremity of that ridge, several hundred yards in rear of the General. All was quiet in the lines of the enemy. There was another ridge south of the one on which General Smith was standing, and separated from it by a deep and very narrow valley. The sides of both ridges were precipitous; their tops sloped gently to the enemy's line.
General Smith informed me that Riley's brigade would pass partly beyond the extremity of the second ridge; then face to the left, and attack a strong Mexican detachment which was in position on that ridge, several hundred yards in rear of their works. Riley was ordered to drive that detachment and pursue it closely into the Mexican main lines. Cadwallader's brigade would go on when Riley faced to the left; and, as soon as he passed Riley, Cadwallader would also face to the left and come into action on Riley's right. Smith's own brigade would turn to the left before reaching the extremity of the second ridge. The Third Infantry and First Artillery would advance in the deep valley between the two ridges; whilst the Rifle Regiment, with the engineer company leading, would ascend the steep slope of the second ridge, and get into position on the flank, or rear, of the Mexican detachment which Riley was to attack in front. In the meantime the head of Smith's brigade had come within view, near the foot of the steep slope of the second ridge, and was moving towards the Mexican main line.
General Smith pointed out to me the route to be taken to reach the top of the second ridge; and ordered that the engineer company and rifles should bear to the right, and on getting near the Mexican detachment, remain concealed, and quiet, until Riley's brigade became well engaged; then join in the attack and pursuit of that detachment.
With these specific instructions, I was ordered to rejoin my company; and Lieutenant Beauregard was directed to take general charge of the movements of Smith's brigade. When Beauregard and I reached the top of the second ridge we found we were 50 yards, or less, in rear of the Mexican detachment, which was facing Riley. All was quiet. In a very few moments Riley's fire commenced.
The engineer company, followed by the rifle regiment was then forming in line, under cover, in rear of the Mexican detachment, whose attention was concentrated on Riley, in their front. We were between that detachment and the Mexican works. A small portion only of the Rifle Regiment was in line, when the firing with Riley became very severe, and the order was given for the engineer company and rifles to rise and fire into the backs of the enemy. That fire was very destructive. The Mexicans were astounded; faced squarely about, and in a moment precipitately retreated.
In my official report it is stated that: "Colonel Riley's advance became engaged with a very strong picket, some 300 yards or more from the rear of the [enemy's] battery, near the crest of the ridge; the engineers and rifles came up at once in position to take the picket in rear, delivered a deadly volley within 50 yards, cheered and rushed on. The enemy's force fled; the head of our column crossed the line of their retreat, which brought the right of the column [engineer company and rifles] conducted by Lieutenant Beauregard, in contact with the Seventh Infantry, which formed the left of Colonel Riley's brigade. I went into the enemy's battery with the colors of the Seventh Infantry, my company immediately behind me. The enemy, or at least a portion of them, stood to their guns well, and delivered a fire of grape into our troops when the head of the column was within 25 yards of their pieces. Our troops followed the retreating enemy without halting until they were beyond the reach of our musketry. Lieutenant Beauregard then strongly advised that the troops be halted and formed. A short time afterwards General Twiggs, came up. The pursuit was resumed. At San Angel we had an unimportant skirmish". (Ex. Doc. No. 1, Appendix, p. 68).
The following additional quotations from my official report are not deemed irrelevant:
"In the action of the morning of the 20th—the battle of Contreras—my men acted with great gallantry; their promptness in obeying every order, and the effect with which they used their muskets, entitle them all to the highest praise. In my report to the chief engineer in the field, I shall make special mention of all who, to my knowledge, particularly distinguished themselves. I will mention here, First Sergeant D. H. Hastings, of the engineer company, who, by his gallant conduct and soldiery bearing, in this action, richly deserves promotion to the rank of commissioned officer in the army. Sergeant Hastings was slightly wounded by my side in the battery. Sergeant [S. H.] Starr attracted my particular attention by his gallant and efficient conduct. Sergeant Starr was the ranking non-commissioned officer with the detachment of the engineer company which accompanied Colonel Harney's command at the battle of Cerro Gordo. I would recommend him for promotion [to the grade of commissioned officer in the army]."
"Artificer W. H. Bartlett attracted my particular attention by [his] cool and steady gallantry, Artificer A. S. Read shot the color bearer of the Twelfth Regiment of artillery, and secured the color."
"Lieutenant Foster was at this time, as I have before remarked, detached with a portion of the company; and, at the head of his men, led the Ninth and Twelfth Regiments of Infantry in their attack on the flank of the retreating column at Contreras."