Semi-Spoiler below picture
*SPOILER WARNING*
*SPOILER WARNING*
Semi-Spoiler below, If you are new to PoTCO I urge you to explore the land instead
I don't know if it counts for this quest but as I have been progressing through the game I have noticed that these 'dig' missions are not 'static drop' which means you can find one spot. Dig, wait 2minutes? (how ever long the spot's respawn is set for) then dig again. This tactic does work and I have completed the
"Buried Portraits" mission using only one dig sight for each island