Final answer:
The Pleistocene-era lake that occupied Death Valley was known as Lake Manly. It points to historical climate shifts and the geological impact of tectonic and glacial activity.
Step-by-step explanation:
The huge lake that filled Death Valley during the Pleistocene time was Lake Manly. This now-dried lakebed provides evidence of a time when the climate in the western U.S. shifted from cool and moist to warm and arid as Earth emerged from the last Ice Age.
The presence of large bodies of water such as Lake Manly, which have since disappeared, indicates significant changes in climate and geography over millennia due to factors like tectonic activity and glacial movements.