Question: What is the city where the The Circle of Oak and Mistletoe (O&M) resides named after?

Context paragraphs:
Oak Ridge Military Academy: Oak Ridge Military Academy (ORMA) is a college-preparatory military school in northwestern Guilford County, North Carolina.  The academy is located within the town limits of Oak Ridge, North Carolina, which is named after the school.  It is seven miles north of the Piedmont Triad International Airport and Interstate 40, and is approximately eight miles northwest of Greensboro, North Carolina's third-largest city.

Columbus Circle: Columbus Circle, named for Christopher Columbus, is a traffic circle and heavily trafficked intersection in the New York City borough of Manhattan, located at the intersection of Eighth Avenue, Broadway, Central Park South (West 59th Street), and Central Park West, at the southwest corner of Central Park.  It is the point from which all official distances from New York City are measured.  The name is also used for the neighborhood a few blocks around the circle in each direction.  To the south of the circle lies Hell's Kitchen, also known as "Clinton", and the Theater District, and to the north is the Upper West Side.

Thousand Oaks, California: Thousand Oaks is a city in southeastern Ventura County, California, United States.  It is in the northwestern part of the Greater Los Angeles Area, approximately 35 mi from Downtown Los Angeles and is less than 15 mi from the Los Angeles city neighborhood of Woodland Hills.  It was named after the many oak trees that grow in the area, and the city seal is adorned with an oak.

Kiest Park: Kiest Park is a 263 acre park in southern Dallas, Texas, United States, established in 1931 by Edwin John Kiest, publisher of the Dallas Times Herald and a member of the Dallas Park Board in the 1930s who donated the land for the park, which was named in memory of his late wife Elizabeth.  It is the largest City of Dallas Park in Oak Cliff and features hike-and-bike trails, tennis courts, baseball diamonds, playgrounds, picnic tables and several Works Progress Administration-era structures, including stone gates at three entrances to the park, a stone picnic shelter and a stone field house.  The WPA also built a formal garden at the heart of Kiest Park.  A pergola was built at the head of the garden in 1934 with WPA funds but fell into ruin and was cleared away.  The nonprofit organization Friends of Oak Cliff Parks restored the historic garden and the City of Dallas rebuilt the pergola in 2014, using $2 million in bond funds, based on the original plans.

Twelve Oaks: In Margaret Mitchell's novel "Gone with the Wind", Twelve Oaks is the plantation home of the Wilkes family in Clayton County, Georgia named for the twelve great oak trees that surround the family mansion in an almost perfect circle.  Twelve Oaks was described as a "beautiful white-columned house that crowned the hill like a Greek Temple," having true southern charm and whimsy.  Margaret Mitchell came up with the idea for The Twelve Oaks, and modeled the home after an actual antebellum mansion located in the historic area of Covington, Georgia.  The home that was portrayed as Margaret Mitchell's Twelve Oaks in the film "Gone with the Wind" has been renovated and is now open as a bed and breakfast and event facility in Covington, Georgia, thirty minutes east of Atlanta.

Lonoke County, Arkansas: Lonoke County is a county located in the Central Arkansas region of the U.S. state of Arkansas.  As of the 2010 census, the population was 68,356, making it the eleventh-most populous of Arkansas's seventy-five counties.  The county seat is Lonoke and largest city is Cabot.  Lonoke County was formed on April 16, 1873 from Pulaski County and Prairie County, and was named as a corruption of "lone oak", after a large red oak in the area that had been used by a surveyor to lay out the Memphis and Little Rock Railroad.

George West, Texas: George West is a city in Live Oak County, Texas, United States, and named for cattle rancher George Washington West.  The population was 2,524 at the 2000 census.  It is the county seat of Live Oak County.  George West was named the "storytelling capital of Texas" in 2005 by the Texas Senate; and it hosts the "George West Storyfest", a festival that features storytelling, cowboy poetry, and music.  Numerous ranches surround George West.

Centennial Circle: Centennial Circle is a five leg roundabout in downtown Glens Falls, a city in Warren County, New York.  The circle is at the intersection of U.S. Route 9 (Glen Street), New York State Route 32 (NY 32, named Warren Street), NY 9L (Ridge Street) and Hudson Street.  Centennial Circle is the site of a formerly signalized intersection, which was replaced with the current layout in 2007.

City of Onkaparinga: The City of Onkaparinga is a local government area (LGA) located on the southern fringe of Adelaide, South Australia.  It is named after the Onkaparinga River, whose name comes from "Ngangkiparinga", a Kaurna word meaning women's river.  It is the largest LGA in South Australia, with an estimated population of 164,800 people in both urban and rural communities and is also geographically expansive, encompassing an area of 518.3 km².  The council is headquartered in the Noarlunga Centre with area offices situated in Aberfoyle Park, Woodcroft and Willunga.

Circle of Oak and Mistletoe: The Circle of Oak and Mistletoe (O&M) is a Wiccan teaching coven based in Flagstaff Hill in the City of Onkaparinga; and an online teaching group and community.  It is the founding coven of the Community Church of Inclusive Wicca which was incorporated in South Australia in 2008.  Whilst primarily a group for Australian practitioners, it has evolved into a provider of teaching services globally.

Supporting paragraphs: Circle of Oak and Mistletoe City of Onkaparinga
Answer: the Onkaparinga River