The best alternative transition to use in place of the underlined transition "for example" in this excerpt is "for instance."
So the revised excerpt would read:
"The importance of national parks to American morale should not be underestimated. Most Americans feel a certain pride when they discuss the beauty and historical significance of these national treasures. For many Americans, the Rocky Mountains, for instance, are massive in size, offer a majestic landscape, and symbolize the American frontier spirit."