Roman Catholic Diocese of Helena Roman Catholic Diocese of Helena The Diocese of Helena () is the Catholic diocese for western Montana with its cathedral located in Helena, the state capital. The diocese was erected from the year-old Vicarate of Montana on March 7, 1884, while Montana was still a territory. The diocese is a suffragan of the Archdiocese of Portland, which encompasses Oregon, Idaho, and Montana. Before becoming a diocese, this was the Vicariate of Montana (covering the whole territory and then state of Montana). For its first twenty years, the diocese served all of Montana. In 1904 the new Diocese of Great Falls-Billings
Helena River catchment Nyaania Creek and on the southern side Piesse Brook are significant in their moving through built up areas which makes them susceptible to urban environment issues. Upper Helena catchment (i.e. above Mundaring Weir) has on the north side of Lake C.Y. O'Connor (formerly the Helena River Reservoir) a range of named creeks that occur in State Forest no 71 and 13: In the higher ground the Helena River passes mainly through State Forest or reserve. This has been beneficial for some of the catchment area, as it has been an important buffer between the urban settlements in the Mundaring