When the state of Colorado ordered its residents to shelter in place in response to the spread of coronavirus, writers Pam Houston and Amy Irvine-who had never met-began a correspondence based on their shared devotion to the rugged, windswept mountains that surround their homes, one on either side of the Continental Divide. As the numbers of infected and dead rose and the nation split dangerously over the crisis, Houston and Irvine found their letters...