At some point (probably in 1975 give or take a year) Uther granted many of his loyal servants their own fiefs. Since the original Blackmoor area was already occupied, the new fiefs were created in the south. An area we called "province one". Dave simply placed the map from Avalon Hill's "Outdoor Survival" game next to the Blackmoor map and showed us which hex had our new fief in it. The area was roughly where the Eastern Hak is located on "modern" maps of Blackmoor. This would probably have been an area that had been secured from the Thonian Empire by the Kingdom of Blackmoor in the War for Blackmoor's Independence (that's speculation on my part as I don't really remember anymore). We then spent many gaming sessions exploring and securing our new Baronies and their surrounding areas. Newgate was originally located there. It was the first fief you came to as you traveled into the area from Blackmoor, so it was referred to as the gateway to the new region and its name became Newgate. Svenny was very active and systematic in searching the area surrounding Newgate to destroy all of the evil or dangerous creatures in the vicinity. Trying to make it a safe place...Svenson provided additional details, in this discussion thread, from 2014:
When Dave expanded the outdoors part of the campaign, he added the Outdoor Survival map to the south side of the main Blackmoor area map. That was originally where Newgate was along with the fiefs of the Snider brothers and Bob Meyer and somebody else.
A map of "The Northern Marches" (the original map used for Blackmoor, from the Secrets of Blackmoor Facebook page, (Dec 30, 2016) in relation to the Outdoor Survival map, where "the exiles from Blackmoor set up shop after the bad scene at Lake Gloomy"
Dave Arneson summarizes the events which took place on the Outdoor Survival map in "The First Fantasy Campaign" (FFC, 1977):
On the Outdoor Survival board, borders appeared half way between the various players' Castles, and roads were built also. Major border changes occurred when Monson was wiped out and the entire area where John Snider held sway was covered in a deadly yellow mist (no one knows what happened inside John's area and no one has come out!). Significant events included a Nomad attack from the Duchy of Ten that was wiped out by Svenson and the Sniders. A great Peasant revolt that wiped out Monson, badly hurt Nelson and was then wiped out by all the other players. An expedition to the City of the Gods (located in the Desert south of Monson's old place) which cost several players' lives (Nelson and Gaylord) plus their holdings going evil. Then the expedition to the home of Father Dragon that took out both Sniders, although an offspring took over Richard's holding.
from "The First Fantasy Campaign" (1977)
I'm uncertain whether any Blackmoor scholars have taken a stab at locating the various players' castles, which desert represents the Valley of the Ancients* (where the City of the Gods is located), or the home of Father Dragon (its location on the map is implied).
*update - see this thread at The Comeback Inn for discussion regarding the possibilities
In his blog post "The Howling Wilderness" from 2014, Daniel Boggs demonstrates how the Wilderness Wandering Monsters tables in OD&D vol 3 The Underworld & Wilderness Adventures were probably derived from the wilderness "Encounter" Matrix I, reproduced in the FFC.
In addition, rules for "evading" based on party size and movement rates (at 5 miles/hex) appear to have their basis in Arneson's Blackmoor. In fact, "Outdoors in Blackmoor" (FCC, 1977) could serve as a precursor to "The Wilderness" section in OD&D vol 3.
Some rules in OD&D are taken directly from "Outdoor Survival", namely terrain penalties for movement, and rules for becoming lost. These would reappear in the D&D Expert Set (Cook/Marsh, 1981; Mentzer, 1983), which became associated with wilderness adventures.
Finally, there are rules in "Outdoor Survival" for wilderness encounters (occurring on a roll of 5 or 6). Arneson based the likelihood of an encounter on the size of the party, whereas Gygax modified the chances of an encounter based on the terrain type.