Twenty-five potassium–argon ages were obtained from granitic rocks in the Endako area of central British Columbia which are presumed to be genetically related and known collectively as the Topley Intrusions. Most of the ages cluster around 138 m.y. but some are as old as 155 m.y. and one is only 114 m.y. These data might indicate either one protracted perhaps intermittent magmatic event culminating in early Upper Jurassic or three separate and unrelated events. In either case the isotopic age is some 40 m.y. less than the age previously assigned to the Topley Intrusions on a basis of apparently good geological evidence.

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