Three of Scotland's tries came from hooker Ewan Ashman, who touched down from a series of line-out mauls, with George Horne, Matt Fagerson and Duhan van der Merwe - tying the men's national record of 27 tries - adding the others. Adam Hastings converted five of them, Ross Thompson the other.
Tommaso Boni's first-half converted try was USA's only reward for their efforts in a game played in tricky conditions.
The Scotland squad now head for South America, where they play two further Tests against Chile (20 July) and Uruguay (27 July).