The following from the CPRR Museum shows the SF News Letter and California Advertiser issues (or portions):
Saturday, May 1, 1869, p 1
Saturday, May 8, 1869, p 1
Supplement, Saturday, May 15, 1869, pp 1-4
The second and third issues include an engraving of the News Letter's spike. The third issue includes an extended recount of the events at the ceremony (carefully blurring that there was more than one golden spike present) The Hewes spike is only directly mentioned in the second issue by quoting a brief item from the Bulletin.
The third issue continues by reprinting what appears to be a report documenting the entire Central Pacific, including enumerating structures. Interestingly this report does not mention turntables and roundhouses at Promontory, but rather at Ogden City, reported as the junction. The report also enumerates the length of all bridges and tunnels.
In the third issue on pg 4, upper right corner, in a section titled "The Summit Deserted - A Scramble for the Relics", in the last sentence is an interesting comment. "One of the presentation spikes was afterwards cut, and half of it given to Dillion as a memento." Was this the end of the SF New Letter's spike?
But there is more. Scrolling below the above newspaper pages is a photo of a spike that the owner thinks might be the original SF News Letter spike - or a close copy. Our belief in this claim rests partly on how accurate we thing the SF News Letter engraving is. The engraving shows a flat sided spike (as some designs at that time were), while the photo of the existing spike is fully headed.
There is an additional SF News Letter source, also. I came across a set of sites reprinting articles by the San Francisco News Letter and California Advertiser from 1881. They mostly talk about Thomas Hill's Last Spike painting, but also include an engraving (I think it may be from the same photo as the 1869 engraving, but appears to be possibly a new engraving) of the gold spike that the News Letter provided in 1869. This is in the second site listed below.
February 12, 1881
The second and third sites also provide a bit of revisionist history, again supplanting the Hewes spike with the SF News Letter spike, and claiming the prayer before the "driving of the spikes" for Marriott of the New Letter instead of Todd.
I'd welcome thoughts on all of this.