Sir Denis Mahon and Nicholas Turner have kindly confirmed the attribution on studying the drawing in the original.
This drawing can be dated with some precision to the artist's time in Rome in the early 1620s since the verso shows a stylized escutcheon with the arms of Guercino's Bolognese compatriot Pope Gregory XV Ludovisi (reigned 1621-23). It was Gregory's election which drew artists from Bologna to Rome in the hope of rich commissions. Such a dating would put this drawing among Guercino's earliest known landscapes. Sir Denis suggests that the drawing on the verso may be by Cristoforo Serra (died before 1678), with whom Guercino shared lodgings in Rome.