Forty-two east-west aeromagnetic lines were flown across the Cook Inlet-Susitna Lowland between Chelatna Lake and Seldovia at a flight altitude of approximately 2,500 feet. The lines traverse all or part of five Mesozoic tectonic elements that dominate the structure of the Cook Inlet area. Each of these tectonic elements, the Alaska Range geosyncline, the Talkeetna geanticline, the Matanuska geosyncline, the Seldovia geanticline, and the Chugach Mountains geosyncline, has a characteristic magnetic pattern.
The aeromagnetic data, compiled as total intensity aeromagnetic profiles, show several significant features which are consistent with the structural grain of the area. A two-dimensional anomaly was observed near the east edge of the area on all but the southernmost profiles, where it becomes obscure. Geologic evidence suggests that this feature, the Knik Arm anomaly, is produced by plutonic rocks that have been intruded along the Seldovia geanticline. Southeast of this anomaly the profiles are almost flat. This flatness indicates that magnetic rocks are deeply buried in this area, which is underlain by slate and graywacke deposited in the Chugach Mountains geosyncline.
