[quote="Bunuel"]
Many of them dug during the Greenwood copper boom a century ago, the hills to the east of Death Valley, Arizona, are dotted with hundreds of copper mines.(A) Many of them dug during the Greenwood copper boom a century ago, the hills to the east of Death Valley, Arizona, are dotted with hundreds of copper mines.
-- incorrectly referring that the hills were dug
(B) Dug during the Greenwood copper boom a century ago, the hills to the east of Death Valley, Arizona, are dotted with many hundreds of copper mines.
-- incorrectly referring that the hills were dug
(C) Hundreds of copper mines, most of them dug during the Greenwood copper boom a century ago, are dotting the hills to the east of Death Valley, Arizona.
-- are dotting refers to a present work they are performing while it is a standard fact
(D) The hills to the east of Death Valley, Arizona, are dotted with hundreds of copper mines, most of them dug during the Greenwood copper boom a century ago.
-- correct(E) The hills to the east of Death Valley, Arizona, are dotted with hundreds of copper mines, most of which are dug during the Greenwood copper boom a century ago.
-- "are" would not be the correct tense
Option D