Emeral Lake, Yukon

There doesn't appear to be a place name on the postmark, but the date is 24 March 2009.
Emerald Lake, Yukon
Emerald Lake, located on the Klondike Highway between Skagway, Alaska and Whitehorse, Yukon, is also known as Rainbow Lake.  The rainbow-like colours result from the blue-green light waves reflecting from white sediment  on the lake bottom.

Yukon is at the northwest corner of Canadan, bordering Alaska.  Until 1896, the border between alaska and Yukon was poorly defined.  That all changed when gold was found in Klondike region, and the gold rush began.