BEEN THERE: I rode a bicycle around this stadium in July 1989, and peeked inside through the opening in the southeast corner, i.e. 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 a large bleacher section was added in right field, but its main purpose was to accommodate the Denver Broncos, one of the eight original American Football League franchises. Including temporary bleachers set up in left field, the seating capacity was raised from 19,000 to 34,000. After the city of Denver took possession in 1968, second and third decks were added on the west side, raising the capacity to just over 50,000, thus satisfying league requirements. Two or three rows of seats were added to the lower deck as well, putting some fans behind structural support beams. In December of 1968, the name was changed to "Mile High Stadium," as its football function became paramount. In 1976 the north (third base) side of the grandstand was torn out and rebuilt, adding two upper decks, changing the grandstand angle from acute to perpendicular. Accordingly, the baseball diamond was rotated counter-clockwise. In the 1977 a new triple-decked movable section on the east side 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 145 feet back and forth across left field. It took about two hours to complete the transition each time. From the late 1970s until the 1990s, the baseball infield was grass except for the pitcher's mound and the areas around each base. (The Denver Bears were renamed the Zephyrs in 1985.) In 1986, luxury skyboxes were added to the top of the third deck.
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 (east) 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 very little 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. Mile High Stadium was one of only eleven major league baseball stadiums without any roof. (Five of those were temporary venues, including Mile High, in use while a new stadium was under construction.) On the downside, there were frequent plumbing problems here, in part due to the technical difficulty of keeping pipes connected to the movable east grandstand. 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 (Coors Field) neared completion.
In addition to many rock concerts over the years, Mile High Stadium hosted an outdoor mass celebrated by Pope John Paul II in August 1993, during the Rockies' inaugural year.
Mile High Stadium was the home of the Colorado Rapids (Major League Soccer) team from 1996 to 2001. A regulation-size soccer field would leave less than 20 feet along the side lines in the football configuration, so they may have played soccer there in the baseball configuration, with the east grandstand retracted.
Given the tremendous fan support they received over the years, it was fitting that the Denver 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! A special feature that was useful for football games was an electrical field heating system that kept the turf green into the winter months. The Broncos continued playing in Mile High Stadium until December 2000, and then moved into their new stadium (originally called "Invesco Field at Mile High") right next door. It was renamed "Sports Authority Field at Mile High" in 2013, approximately. In early 2002 demolition of Mile High Stadium began, after it was deliberately set on fire by an incendiary bomb as part of a terrorism response drill. Virtually nothing was left of the old place by the end of March.