A night in November to December of 1838, priestly Imperial Prince Soncho, who was then the head priest of Chion-in, had a dream in which a bevy of swans flew to the small mountain at the back of Isshin-in; he believed it was a good omen, and thus gave Isshin-in Temple the sango 'Gunsenzan,' since it had no other.
天保9年10月（1838年11月～12月）のある夜、時の知恩院門主であった尊超入道親王が、夢の中で白鶴の群れが一心院の裏山に飛来する光景を見て吉祥と感じ、当時山号のなかった一心院に「郡仙山」の山号を名付けた。