The Tesoro Escondido Agate — literally "hidden treasure" — deposit was discovered in 2010. These agates are infillings of amygdales primary hosted within andesitic volcanic rocks. The agates here are found with two different skins: the predominant variety is green, the other has a reddish–brown exterior. The green is most likely host rock which is weathered off of the reddish–brown skinned variety. The Tesoro Escondido agates are banded and strongly colored -- often with contrasting colors. The color range of these agates includes red, yellow, orange, and occasionally: blue, green, and violet. Many different sizes are found here. Most of them are in the medium range: 2"x 2.5" to 4"x 3" and an average of 0.5 lb. to 1.5 lbs. The more extreme ends of the gamut (small and large) are fewer in number. The smaller ones are usually 1"x 1" to 1.5"x 2" and range in weight from 0.2 lbs to 1/3 lb.; and the large agates found here are 5"x 3" to 7"x 9" and weight anywhere from 4 lbs. to 8 lbs.
This source is near Cañon del Atuel, high in the mountains, and a rugged climb. There are surface agates in this area, but the best material is underground. Miners must climb high mountains with backpacks, hand–tools, and supplies. They must then mine the agates by hand. Finally the workers must descend the mountains with 15 to 40 kilogram (33 to 88 pound) sacks full of agates -- if the dig is successful. If not, they must still endure the climb and descent. In addition to these challenges, heavy snows blanket this area during the winter. The agates can only be mined during the thaw.