It was a standard right here in NYC, Leslie West is from the New York area. Nantucket Sleigh Ride was a song on one of Mountain's albums. I was fortunate to have seen them play more than a few times. West's tone was incredible, reminding me of Sonny Rollins. They were able to use West's size as a gimmick, but I suspect that poor health was in large part at the root of their departure, not any lack of chops or talent.
