Related Clues:

• Gold in them thar hills?
• Feldspar, e.g
• Underground resource
• Mineral in a wall, perhaps
• 10-Down source, e.g
• Forty-niner's pay dirt
• 4-Down contents
• Argentite, e.g
• Stitcher's line
• Sought-after rock
• Tram car filler
• Valuable extraction
• Forty-niners' score
• Bed rock?
• Deposit of a sort