Kirby Smith made a speech published by the Galveston Tri-Weekly news on May 30, 1865 (I have paraphrased)
"..I intended to struggle on to the last with an army united in purpose, firm in resolve, and battling for the right, I believed that God would yet give us the victory. I reached here to find the Texas troops DISBANDED, and hastening to their homes.....I am left a commander without an army, a General WITHOUT TROOPS. You have made your choice......"
Three days later, on June 2, Smith surrendered the Department of Trans-Mississippi.
SOURCE: To the Tyrants Never Yield, Kevin Young, Wordware Publishing, 1992
The troops guarding Houston disappeared on May 23, 1865, as these old posts of mine below indicate. The information came from the Galveston Daily News.