Here is a portfolio of small postcards I found.
The copyright is 1974 but someone has dated it 7/2/77.
On the back:
"SPIRAL OF EXCITEMENT The Big Bend, traveling at speeds up to 55 mpg, provides thrill for thousands of visitor to SIX FLAGS Over Texas. The huge ride is one of the most popular at the big theme park."
On the back:
"EL ASERRADERO (THE SAWMILL) or the SIX FLAGS OVER TEXAS famous "Flume Rid" has been called the most popular and exciting ride very devised--here the "Hollow Log" plunges down the water flume. "
On the back:
"TEXAS EXCITEMENT Excitement -- Three of the most popular rides at SIX FLAGS Over Texas are shown in action. At the top is the Runaway Mine Train which annualy carries more than 2 1/2 million riders. At center an authenci 1898 steam engine carries passengers over a narrow gauge track which encricles the huge theme park. And, in the foreground is the SIX FLAGS Mini Mine Train, designed for the younger set."
One the back:
"A picturesque roadway seen by guests who dirve their own minature ANTIQUE CAR."
One the back:
"One off Six Flags' REAL STEAMSER which once saw service on a Louisiana plantation in early 1900.
On the back:
"Six Flags Over Texas is a wonderland by night as lights twinkle in hundreds of trees and the dandelion fountain becomes alive with color.
On back:
" GOTACH -- Young guest at Six Flags Over Texas pursue one another "through the sky" aboard Cyrus Cosmo's Flying Machines. Topped by a sculpture of the theme park's popular Cyrus Cosmo character, the ride is a favorite among the entertainment center's younger guests. More than than 2 million persons visit Six Flags Over Texas each year."
On the back:
"Towering 200 feet into the sky, the Texas Chute Out carries rides to a height of 175 feet before their parachutes "break loose" and drop at free-fall speed for more than three stories. THen the chutes billow and begin to slow the ride for a soft landing. The huge parachute drop is a landmark at Six Flags Over Texas."
On back:
"The flags of the U.S. Republic of Texas, Confederacy, Mexico, France and Spain flutter in the night sky over the entrance mall at Six Flags Over Texas."