The Carp Hills are unique within the City of Ottawa. An island of 1 billion year old rock rising above fertile farm land deposited by the Champlain Sea, they extend approximately 13 km long and 3 to 4 km wide, comprising nearly 4,000 hectares (~10,000 acres), which makes them the second largest natural area within Ottawa.
Most of the Carp Hills is designated a candidate, Regionally Significant Life Science Area of Natural and Scientific Interest (ANSI). However, an area roughly 1300 ha in size located in the southeastern third of the Carp Hills – called the Carp Barrens – has a higher candidate designation of Provincially Significant Life Science ANSI due to the combination of ponds and rock barrens that lie at the surface, creating a rare ecology for unusual plants.
The area was first identified as significant in a Ministry of Natural Resources ANSI report (Brunton 1995) for its complex mix of forest, Precambrian Shield rock barrens, high concentration of regionally significant species, wetland complexes, and overall high level of ecological integrity. In the 1997 Natural Environment Systems Study (NESS) conducted for the former Regional Municipality of Ottawa-Carleton (Brunton 1997), the Carp Hills Natural Area (Area 538) was identified as one of the most significant areas in the municipality for maintaining biodiversity and ecological function, as well as for its outstanding examples of granitic bedrock barrens.
The Carp Hills are also a Provincially Significant Wetland (PSW) Complex. The wetland areas are zoned as PSW in the City of Ottawa’s Official Plan.
The Carp Hills are an island of Precambrian rock set in a sea of Paleozoic limestone. The Hazeldean Fault runs on the Hills’ southern edge along Carp Road (GSC Map 1508A) where the Precambrian rock formation was thrust up above the limestone (likely during the Mesozoic Era), which is now overlaid with fertile Champlain Sea sediments in the farm fields around Carp. The highest points on the ridge occur along this fault line, which runs northwest/southeast, causing most water on the ridge to drain to the northeast (towards Dunrobin). While some small streams along its southern edge flow south into the Carp River, the Carp Hills are primarily part of the watershed that drains into Constance Lake through many watercourses like Harwood Creek.
The Gatineau Hills across the river in Quebec are made from the same Precambrian formation, uplifted along the Eardly fault (Geology of the Ottawa Area).