I wasn't aware of the identifying features but once you see them they become obvious. Steve pointed out the silvery green underside of the leaf with its distinctive silver scales. distinctive if you know what to look for. The twigs are light brown with prominent silver and brown scales. The older, thicker branches are armed with sharp thorns.
|Note brown scales, thorns|
|Silver scales- Click to enlarge|
"It was studied in the 1940s by the Soil Conservation Service, and the strain 'Cardinal' was released in 1963 for commercial propagation. In the eastern and central United States, autumn olive was planted to provide food and cover for wildlife, as screens, windbreaks and barriers along highways, to stabilize and revegetate road banks, and to reclaim mine spoil. For some years after planting the plant seems contained, but then it suddenly becomes invasive and difficult to control." MDC
This MDC site has comprehensive information about control.