growth rate of 66.0%. The 1973 oil embargo by OPEC spurred an oil boom in eastern Montana, northern Wyoming and Western North Dakota. With this increase in oil production, Billings became the headquarters for energy sector companies. In 1975 and 1976, the Colstrip coal fire generation plants 1 and 2 were completed; plants 3 and 4 were operational in 1984 and 1986.
In the 1970s and 1980s, Billings saw major growth in its downtown core; the first high-rise buildings to be built in Montana were erected. In 1980, the 22-floor Sheraton Hotel was completed. At the time, it was the tallest building from Minneapolis, Minnesota to Seattle, Washington and from Denver, Colorado to Calgary, Alberta (Canada). Upon its completion it was also declared "the tallest load-bearing brick masonry building in the world" by the Brick Institute of America. During the 1970s and 1980s, Billings also saw the completion of other important buildings in its downtown core; the Norwest Building (now Wells Fargo), Granite Tower, Sage Tower the MetraPark arena, the TransWestern Center, many new city owned parking garages and the First Interstate Tower, now the tallest building in a five state area.
With the completion of large sections of the interstate system in Montana in the 1970s, Billings became an even bigger shopping destination for an ever increasingly larger area. The 1970s and 1980s saw new shopping districts and shopping centers developed in the Billings area. In addition to the other shopping centers developed, two new malls were developed and a third mall redeveloped and enlarged, Rimrock Mall on what was then the city's west end, Cross Roads Mall, no longer in existence, in Billings Heights, and West Park Plaza mall in midtown. In addition, several new business parks were developed on the city's west end during this period. Billings was affected by the 1980 eruption of Mount St. Helens in May; the city received about an inch of ash on the ground. The Yellowstone fires
