BEEN THERE: I rode a bicycle around this stadium in July 1989, and peeked inside through the opening in the southeast corner, what would have been right center field.
Although a football stadium by every appearance, Mile High Stadium actually began its existence as a baseball stadium, built for the minor league Denver Bears in 1948. The two wings of Bears Stadium's unroofed single-deck grandstand were originally positioned at an acute angle, bearing a strong resemblance to Seals Stadium. In 1960 the seating capacity was raised from 19,000 to 34,000 to accommodate the Denver Broncos, one of the eight original American Football League franchises. After the city of Denver took possession in 1968, a second deck was added, raising the capacity to 50,000. (I'm guessing that this was when the north (third base) side of the grandstand was rebuilt, changing the grandstand angle from acute to perpendicular.) In December, the name was changed to "Mile High Stadium," as its football function became paramount. In the 1977 a new triple-decked movable section was added, and Mile High Stadium assumed its final form -- the classic football "U" shape, though more squared compared to Memorial Stadium. This brought its seating capacity up to 76,000. That triple-decked section moved on a cushion of water, sliding more than 120 feet back and forth across left field. It took about two hours to complete the transition each time.
Given the fact that the minor league Denver Bears could never hope to fill even half of all those seats, this costly technological marvel was obviously designed to attract a major league baseball franchise to Denver. Unfortunately, however, the Mile High City lost out to Seattle and Toronto in the 1977 franchise expansion round, casting doubt on the wisdom of the whole movable grandstand idea. Over a decade passed before the folks in Denver finally got their wish, along with Miami -- but NOT Washington! Seldom has baseball fever reached a higher pitch than when the Colorado Rockies began playing in the spring of 1993. Mile High Stadium set a National League record for regular game paid attendance on April 9, 1993 -- 80,227 -- and a total of 4,483,350 fans went to games there that year, smashing the major league baseball attendance records that had just been set by the Toronto Blue Jays. Nevertheless, by the 1990s such multi-use stadiums were hopelessly out of style, so Mile High's days as a big league baseball stadium were numbered from the get-go.
The unadorned triple-decked, bare steel girder dual-purpose structure called to mind Metropolitan Stadium, as did the improvised, incremental process of expansion. Compared to the other football-to-baseball stadiums, Mile High Stadium wasn't really so bad as a venue for baseball games. This was partly due to the fact that the entire left field grandstand moved, rather than just the lower portion of it, as in Dolphin Stadium. Two other features marked this stadium as unique: First, the second deck was very large (which is why the above diagram contains more orange color than any of the other stadium diagrams), while the third deck was quite small, with virtually no overhang. Usually it is the other way around. Also, the outfield dimensions were unusually large: The distance to right field, 370 feet, was longer than any other major league stadium, except for Braves Field in its early days. Nevertheless, because of the thin, dry air, Mile High Stadium set home run records and gained a reputation as a slugger's paradise. Because of the 1994 players' strike, the final baseball game at Mile High Stadium was played several weeks earlier than had been planned, as construction on the Rockies' new home neared completion.
Another special feature (though not useful for baseball games) was an electrical field heating system that kept the turf green into the winter months. The Denver Broncos continued playing in Mile High Stadium until December 2000, and then moved into a new stadium bearing the same name right next door. Given the tremendous fan support they received over the years, it was fitting that the Broncos finally won the Super Bowl while they were still playing at their original home, at the twilight of quarterback John Elway's career -- in both 1998 AND 1999! In February 2002 the old Mile High Stadium was deliberately set on fire by an incendiary bomb as part of a terrorism response drill and was demolished soon afterwards.
SOURCES: Lowry (2006), Pastier (2007), USA Today / Fodor's (1996), Rosen (2001), Washington Post, denverbroncos.com/