Having marched south from Corpus Christi, Taylor reported the first contact between the two armies. Encountering Mexican troops on the west bank of the Arroyo Colorado, Taylor's force was informed by their commanding officer that any attempt to cross the arroyo would constitute a declaration of war, and would be met with force.
HEAD-QUARTERS, ARMY OF OCCUPATION,
Camp 3 miles south of the Arroyo Colorado, March 21, 1846.
SIR: I respectfully report that my forces are now concentrated at this point, the 3d brigade having joined me to-day. We are nearly north of Matamoras, and about 30 miles distant.
The Arroya Colorado is a salt river, or rather Iagoon, nearly one hundred yards broad, and so deep as barely to be fordable. It would have formed a serious obstruction to our march had the enemy chosen to occupy its right bank, even with a small force. On the 19th, the advanced corps encamped within three miles of the ford, and a reconnoissance was pushed forward to the river. A party of irregular cavalry (rancheros) was discovered on the opposite bank, but threw no obstacle in the way of examining the ford. They, however, signified to the officer charged with the reconnoissance that it would be considered an act of hostility if we attempted to pass the river, and that we should, in that case, be treated as enemies. Under these circumstances, not knowing the amount of force that might be on the other bank, I deemed it prudent to make dispositions to pass the river under fire, for which please see my " orders," No. 33. At an early hour on the 20th, the cavalry and 1st brigade of infantry were in position at the ford, the batteries of field artillery being so placed as to sweep the opposite bank. While these dispositions were in progress, the party that had shown themselves the day before again made their appearance. I sent Captain Mansfield to communicate with the officer in command, who said that he had positive orders to fire upon us if we attempted to cross the river. Another party then made its appearance, and passed the river to communicate with me. One of them (who was represented as the adjutant general of the Mexican troops) repeated substantially what had been sent before, viz: that they had peremptory orders to fire upon us, and that it would be considered a declaration of war if we passed the river. He placed in my hands, at the same time, a proclamation of General Mejia, issued at Matamoras a day or two previous, which I enclose. I informed the officer that I should immediately cross the river, and if any of his party showed themselves on the other bank after the passage commenced, they would receive the fire of our artillery. In the meantime, the 2d brigade (which had encamped some miles in any rear) came up and formed on the extreme right. The crossing was then commenced and executed in the order prescribed. Not a shot was fired; and a reconnoissance of cavalry, sent immediately forward, discovered the party which had occupied the bank retreating in the direction of Matamoras. Agreeably to my orders, they were not molested. The cavalry and 1st and 2d brigades of infantry, with a train of two hundred wagons, crossed over and encamped at this point, three miles distant, at an early hour in the afternoon.
I have thought proper to make a detailed report of this operation, as being the first occasion on which the Mexicans have shown themselves in an attitude decidedly hostile. It has also furnished an excellent opportunity for the instruction of the troops, and for displaying their discipline and spirit, which, I am gratified to be able to say, were everything that could be desired.
I am compelled to remain at this point until joined by the supply train of the 3d brigade, which is unavoidably in the rear. On the 23d, at latest, I expect to resume the march, but am not fully decided as to the direction. While Matamoras is the point to be ultimately attained, it is necessary, at the same time, to cover our supplies, which will soon arrive at Point Isabel. From the best information I am able to obtain, the enemy is not in force on this side of the Rio Grande. A few rancheros are still on the route hence to Matamoros. It is believed that there may be nearly 2,000 troops in that place, but what proportion of regular troops I cannot state with confidence. The arrival of General Ampudia is expected from the interior, but the accounts I receive of his movements are quite contradictory.
I am, sir, very respectfully, your obedient servant,
Z. TAYLOR,
Brevet Brig. Gen. U. S. A., commanding.
The ADJUTANT GENERAL of the Army,
Washington, D. C.
