The answer to this question dates back to April 19, 1863 when a fire broke out in a building between Blake and Market Street in what we know today as LoDo. The fire spread rapidly due to the predominance of wooden buildings and destroyed approximately 50 buildings, including stores, hotels, and other businesses along Blake, Market, and Larimer Streets.
After the fire, Denver's residents and city officials realized that the extensive use of wood in construction posed a major fire risk. As a result the Brick Ordinance was born. The ordinance led to a shift away from temporary wooden structures toward more durable and fire-resistant materials, helping prevent future large-scale fires and improving public safety. The ordinance led to a shift away from temporary wooden structures toward more durable and fire-resistant materials such as brick and stone.
Given Denver’s abundance of clay, brick construction was accessible and became the standard of commercial and residential construction for nearly a century to follow. For more information on this piece of local history, check out the below article from Colorado Public Radio.