This verifies a statement that Capt. Joseph Plummer made about the telegraph (they did not have access to it until reaching St. Louis). George Knapp's Wilson's Creek staff ride document gives Rolla as a telegraph connection for Gen. Lyon. However that does not appear to be correct even though the corps apparently built the connection by the end of that August. (Although I still don't have an exact date, this helps explain the bigger picture, and now I understand Capt. Plummer better.)

Extracted from William Plum's history on the telegraph:

"...At this time [July 25, 1861] there was no telegraphic communication between St. Louis and Ironton, or along the line of the Iron Mountain Railroad ; none from St. Louis on the North Missouri Railroad to the Hannibal & St. Joseph Railroad ; none over the South-west Branch of the Pacific Railroad to Rolla, and none west of Jefferson City on the main stem of the Pacific road ; but on the Hannibal & St. Joseph road the line and road itself had been kept open, except when temporarily impaired by guerrillas."

"The telegraph company operating the lines to Booneville was able, on Lyon's advance, to repair their wires, so that by the 21st of June he dispatched telegrams from Jefferson City, and on the twenty-fourth from Booneville, where he remained in telegraphic communication for some days at the head of one invading army, while his chief, on the eve of another campaign, was at Grafton, over seven hundred miles distant, at the head of another. When Lyon left Booneville, July 3, he seems not to have been again in telegraphic communication with any point up to the date of his unfortunate sacrifice in August."