The Select Keys By Time utility lets you select keys within a specified start and end range of time. You can select a large range of time, which might be difficult to select using the mouse in the Track View Key window for example.
This utility works in Curve Editor and Dope Sheet Edit Keys modes.
To use Select Keys By Time:
Track View Utilities, then choose the Select Keys By Time utility from the Track View Utilities dialog. 
When on, deselects all keys before keys within the specified time range are selected.
 In Dope Sheet mode, you can highlight a single track to select all keys in the descendants of the track when Modify Subtree is on (
).