Zoe writes from her Santa Fe trip that this staircase was constructed without nails by a carpenter who showed up in answer to a prayer, built the staircase, and disappeared without accepting payment.
She also told me that it was built as an afterthought because the male choirs used to climb up a ladder to get to the loft and the church had to change that when the ladies joined.
Good intel gleaned from your tour, Zoe!