If you are a home owner in Highlands Ranch, you are a member of the Highlands Ranch Community Association. There are several areas in Highlands Ranch which have their own neighborhood association with a board of directors and an assessment fee which might pay items like common area maintenance or a neighborhood pool. These are considered "sub associations." If you live in a sub association, you pay an HRCA assessment and a sub association assessment.
You can check this map to see if you live in a sub-association. For more information open this list of the Highlands Ranch Sub Associations and their respective contacts.