Here is more of the quote from the US officer: "At Lime station (Calera), this road is crossed by the South and North Railroad, leading from Montgomery to Decatur - of which about twenty miles are completed and in use. The road penetrates the Cahaba coal field and the rich deposits of red hematite of Red Mountain."
Here is more of Armes quote about Brocks: "This gap, a sixty-foot cut of solid rock several hundred feet long, through the backbone of Shades Mountain, was an obstacle Gilmer could not surmount. His contractors, unable to secure powder, put their men on the work with crowbars and wedges. The railroad was graded only as far as Graces Gap during the war. This cut was not finished until two years after the war, under Superintendent J.F.B. Jackson. In 1908 the mountain at Brocks Gap was tunneled by the Louisville and Nashville Railroad authorities."
Don't know where Graces and Brocks are exactly, but roughly the railway from Calera to Hillsboro is about 17 miles, to the Cahaba another mile, and a couple more to Shades Mountain. So based on the 20 mile reference, it does appear that it extended to the Mountain. My point regarding Wilson's order to destroy the Cahaba railroad bridge was just that there would be no reason for such an order if it was not in use. Don't think any of the accounts that mention the bridge describe it as unfinished, but don't think any mention its actual destruction either.