Fourteen aeromagnetic profiles were flown east-west across the Cook Inlet area in 1954, nine extending from about the Triumvirate and Capps glaciers to the Chugach Mountains, and five from

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the Iniskin-Chinitna Peninsula to the Kenai Peninsula. These profiles show several magnetic features that seem to have geologic significance.

The over-all arched character of the profiles suggests a block-shaped rock mass underlying Cook inlet at great depth. A 1,600-gamma anomaly was observed over Mt. Susitna, a granitic intrusion. A two-dimensional anomaly observed over Knik Arm may reasonably be attributed to a zone of buried granitic intrusive rocks continuous with the intrusive cropping out at Eklutna. This intrusive, or zones of intrusives, appears to deepen southward, reaching estimated depths of 5,000-6,000 feet at the lower end of Knik Arm. Anomalies observed over the Susitna flats indicate that the magnetic basement is buried 12,000-14,000 feet.

An abrupt magnetic rise of 300-400 gammas observed over the coast line of the Iniskin-Chinitna Peninsula is caused by a significant change in rock type, suggesting the possible existence of a fault with a vertical displacement of several thousand feet. East of this area, no near-surface anomaly-producing rock masses are present. It is likely that here the depth to magnetic basement is very great.

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