Why is Seattle called the "Emerald City?"

Seattle is often referred to as the "Emerald City" because of the lush evergreen forests and the more than 6000 acres of parks within the city limits".  Where did that nickname come from?  From 1869 to 1982 Seattle was known as the "Queen City," but in the early 1980s, a contest was held to promote tourism and the name "Emerald City" was chosen.   Seattle is also known as the "Evergreen State."