The oldest rocks in California are the ones marked with the letter D.
Explanation:
From the presented geological map and its legend, we can see the different types of rocks, both by composition, and by the period in which they have formed. The easiest way to find out which rocks are the oldest is to look at the period in which they formed. In this case, it is the rocks marked with the letter D, on the map being painted with blue color.
These rocks are older metamorphic and sedimentary rocks. On the legend it says that they have been formed in the Precambrian, Paleozoic, and Mesozoic periods. Compared to the other layers of rocks, which have all been formed between the Mesozoic and the present, these rocks have much longer history.
The rocks of these age are often big advantage for the economy. The main reason for that is that they are often rich with numerous minerals, thus the mining industry can be developed. As seen in practice, most of the mining industry in California is actually where these types of rocks are found, often having deposits of gold, copper, nickel etc.
Learn more about the gold extracted from the mines in California https://brainly.com/question/7298770
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