You have a look through your sensors, and see a conga line of volcanoes weaving up the continent.
Now, your image wouldn't be labeled, of course. But you can see a trench offshore, and a zig-zaggy ridge, so you can sketch in some very small oceanic plates busily subducting beneath the continent. The line of coastal mountains and that volcanic arc, less than a hundred miles from the sea, would have given the game away even if you didn't have super-cool sensors that can see beneath the sea. You know there's an active subduction zone here.
You run further scans. Some of the volcanoes in that arc are fairly young, and have been active in the recent past. You do a quick north-to-south sweep, and notice Mt. Baker still steaming away. Glacier Peak has a 300 year-old coating of ash. Mount Rainier is riddled with hydrothermal anomalies, cooking itself from the inside: it's so rotten you can see evidence of mudflows barely over a decade old. Mt. Adams doesn't seem to have erupted for the past few thousand years, but hydrogen sulfide fumaroles puff away atop it. And, a short jog to the south, Mt. Hood has also got active fumaroles. Any of these volcanoes could erupt at any time. The cities you see, located in the shadows of these restless mountains, had better watch out.
But it's one volcano in particular that's caught your eye (or eyestalk)...