From the Imagineering Disney blog, a wonderful gallery of photos from the construction of Space Mountain at the Magic Kingdom in Walt Disney World. This is the original mountain, beating the Disneyland one to completion by two years:
Although the concept of Space Mountain was originally envisioned for Disneyland, the first Space Mountain to open was at Magic Kingdom at Walt Disney World. After the Matterhorn Bobsleds opened at Disneyland in 1959 and were hugely popular, Disneyland management asked for a second thrill ride. Walt was on board but the plans for this second coaster were delayed for another decade. Disneyland didn't get their Space Mountain until 1977, more than two years after Magic Kingdom got theirs in 1975.