In the book Consecration to St. Joseph, by Fr. Donald Calloway, he writes on page 189 about the miraculous staircase that was built for the Sisters of Loretto in 1873.
He records that in 1996, a study was done by Forrest N. Easley, a forester and wood technologist for the United States Forest Services and the United States Naval Research Laboratory. His extensive study found that the wood of the staircase is spruce, but unlike any other spruce in the world. Additional studies were undertaken, and it was determined that the spruce that most resembles the kind found in the spiral staircase is only found in Israel.