Found this in this particular box with the note, from an Elta Gray... note says:
"24K Gold over .999 silver given me by Tony Korfman(sp?) Owner - only 10 minted"

Another little note in my Aunt's handwriting says, "Cost from Elta $1000 - mark down to 914 - for me - one of 10 gold over sterling silver"

Gold Strike Inn Hoover Dam 1935-1985, $1 gaming token

URL to the reverse of the coin:
http://www.chipguide.com/tcbuploads.php?image=HPNX0082.JPG