When the decrypted Ansom marches on Warchalking after TBfGK, it is a small level 2 city held by Unaroyal and described as being valuable primarily for its farms. It also possesses an orchard and a mill. Its defenses consist of its location on a small hill, an earthen berm capped with stones for an outer wall featuring an iron gate between stone blockhouses, and an inner garrison fortress of logs around a stone tower with a wooden roof.
The side that won the battle vs. Lord Manpower and conquered Warchalking might have been Unaroyal, because they held that city when it was reconquered by Gobwin Knob. Unaroyal Spearman Wrigley indicates that the Marbits "did most of the work at Warchalking", further indication that Unaroyal lead the origional attack.Erf-b1.5-p034
Warchalking is at most 72 hexes from Gobwin Knob. This is based on the distance Ansom and Wanda's army travels on the turns after the volcano eruption. Assuming they left immediately before the end of turn 1, Warchalking is 4 turns or less away. The 3-hex column moves at 18 in order to keep the stacks together. If the column waited until turn 2 to leave, Warchalking would then be less than 54 hexes away. This assumes that all hexes the stack moves through cost exactly 1 movement point for the slowest unit in the column, so it seems likely that Warchalking could be less than 50 hexes from Gobwin knob.
Real World Reference
Warchalking is the drawing of symbols in public places to advertise an open Wi-Fi wireless network.