The Boulders At Katy Trail 471 Hemsath Rd, Saint Charles, MO63303 The Boulders At Katy Trail is a condominium development that is located off of Hemsath Road, very close to the Page…More Avenue 364 extension. Developed by Mills Property, the first phase of this development was started in 2002. In 2009, Phase Two added an additional three buildings to this community. It is perfectly landscaped with trees, fountains and lakes. Sales as well as leases are available.