The term 'Gold Rush Quest' refers to the period of time in the mid-1800s when people from all over the world flocked to California in search of gold. The term is also associated with the mining of ORE, which is a mineral or rock containing valuable metals such as gold. ORE is typically mined through excavation and can be found in many places around the world. The three-letter solution for this crossword puzzle is ORE, which is an abbreviation for the mineral or rock containing valuable metals.