Is the Las Vegas region on Lee windward side or leeward side?

The Las Vegas region is on the leeward side of the Spring Mountains.

The prevailing winds in the Las Vegas region are from the west. As these winds cross the Spring Mountains, they rise and cool, causing moisture to condense and fall as rain or snow on the windward side of the mountains. On the leeward side of the mountains, the air descends and warms, causing any remaining moisture to evaporate. This results in a much drier climate on the leeward side of the mountains, which includes the Las Vegas region.