The best place to find information about the famous Red Dress Run and where to find one in your part of the world is reddressrun.org.  The site provides a single calendar highlighting all the  Red Dress Run events around the globe, as well as the history of the event, including the ‘untold’ story of how it started:

The Hash House Harriers qualify as the world’s largest running club. Despite their size and having been founded in 1938, their Red Dress Run may be the only completely original idea they have ever had. And it happened nearly by accident.

On August 7, 1987, a young lady wearing a red dress emerged from an airplane that had landed in southern California to visit a friend from her high school years. Shortly thereafter, she found herself transported to Long Beach, where her friend intended to introduce her to a zany running group called the “Hash House Harriers.” One member, noting her gender and attire, urged that she “just wait in the truck” until her host returned. With that goading, she ran into history sporting her red dress and heels.

The following year (August 12, 1988), to commemorate the event, the San Diego Hash House Harriers sent “The Lady In Red” an airline ticket to attend the inaugural Red Dress Run. Hundreds of male and female hashers adorned themselves in red dresses for a spectacle widely covered by California newspapers and TV news. In addressing the crowd, The Lady In Red suggested that Hash House Harriers hold the Red Dress Run annually as an occasion be used to raise funds for local charities.

The Red Dress Run hash tradition has a strong focus on fundraising for charity; the New Orleans Red Dress Run, for instance, provides Red Dress block grants of up to $5,000 for qualified local 501c3 groups that apply.