LOVER IN THE ROUGH by Elizabeth Lowell was originally published as a Silhouette Intimate Moments but has been republished many times. I don't have the original cover but one of the reprinted versions. I have some of her books, including this one, on my keeper shelf.
Reba Farrall was lost—until a kindly old gentleman took her under his wing and helped heal her shattered spirit. Now her dearest friend is gone, leaving her with a doubting, broken heart...and half-interest in a California gem mine.
But Chance Walker has burst into Reba's life—a daring adventurer who believes in nothing except the priceless uncut stones for which he searches the Earth. In the blistering heat of Death Valley—in the intoxicating presence of a jewel more exquisite than any he has ever seen—Chance must confront a dire peril that stalks the sad and sensuous beauty. For only he can save Reba Farrall from harm—and only she can teach him how to love.