John, I do think you are on to something. It seems reasonable that Bowen communicated with Jackson via some eastern route after the telegraph failure on the 29th. But I have a few rambling thoughts and questions.
Assuming Bowen had two means to telegraphically communicate with Pemberton from GG —one to the east and one directly to the north, then….
If GG—>Vicksburg line went down during the GG bombardment on April 29, why was Bowen unable to immediately reroute messages from GG to the Port Gibson—> Gallatin—> Jxn—> Vicksburg route in a timely manner? Why the long delay during the bombardment of GG? It seems communication was down most of the day.
Thus…
Is it possible that the telegraph breakdown actually affected the entire line from PG—>GG—> Vicksburg? In other words, the break was not just between GG and Vicksburg but occurred in a way that affected the entire line from PG to Vicksburg? This would make more sense when it is declared that a retreat across Bayou Pierre (as opposed Big Black) would entail a loss of all communication.
My other query involves the message by Pemberton from Vicksburg to Loring on May 2, sent when Loring and Tilghman were moving from Edwards to Port Gibson. I'm not sure the precise route that they took, but I'm assuming they travelled south from Edwards across 14-Mile Creek and then toward Cayuga/Rocky Springs. Pemberton probably sent this message from Vicksburg via courier with hopes of intersecting Loring somewhere between Cayuga and Rocky Springs.
Anyhow, that message, in part, reads:
"Nothing has been heard from General Bowen since 5.30 last evening. My anxiety to hear is very great, and I hope you will keep me constantly and regularly informed of your position and current events. If possible, stop the telegraph wire behind you, which can be done if the telegraph operator took with him his instruments."
We are all familiar with this message but I wonder what "stop the telegraph wire behind you" means?
And is the telegraph operator with Loring as he marches from Edwards? Or is he referencing the telegraph operator in Port Gibson, or maybe even Grand Gulf? Pemberton seems to think that whatever the problem is it can be resolved by a telegraph operator who has his "instruments." This is probably not important but something to ponder.
Whatever the case might've been, I was wrong to suppose earlier in this thread that the Confederates might have repaired telegraph communication from Vicksburg to a point near Hankinson's Ferry on the north side of Big Black. It appears that any such communication from Vicksburg to points around Hankinson's Ferry after Loring/Bowen retreated was carried out by a line of couriers, not by telegraph.
But, again, I do think you are on to something. And so I'm wondering if the reason Bowen could not report from GG to Jackson as the Battle of GG raged was because the only telegraph station working was the one in the town of Port Gibson. Thus, he does not report to Pemberton until such time as he was in Port Gibson and then only via the eastern telegraph route.