Travel Rules

Travel and exploration is core to the West Marches style, so we've opted to use custom rules. "Montage" rules cover a week at a time to account for vast distances, and day-by-day rules break down the interesting parts into more detail.

Montage Rules

Each week is covered by a skill challenge, which is passed with 5 successes or failed with 3 failures. Athletics, Nature, and Survival will always be relevant skills, but any skill can be used with enough justification. The Ranger's Natural Explorer feature grants advantage on their first check of each skill challenge. The party can change pace between each check on the skill challenge, with any leftover days at the end taken at the average pace for the week.
Each failure has an increasing chance of causing a random encounter, with at least one encounter guaranteed on an entirely failed skill challenge. A critical failure counts as two failures, The encounters also become progressively more dangerous with each failure. Higher level parties face lower encounter chances in less dangerous areas, and eventually outgrow the skill challenge entirely.

Failures also have other consequences. A single failure may cost the party extra rations or some of the day's progress, while entirely failing the skill challenge might leave them entirely lost. On the other hand, complete success will lead to bonuses like covering extra ground, using up significantly less rations for the week, or happening across some loot.
At the beginning of each week, every party member makes a foraging check for the week. Everyone who fails consumes four days of rations, and everyone who fails by more than 5 consumes seven days of rations. The Outlander background's Wanderer feature grants a +2 to foraging checks and allows them to forage enough food for an additional person when successful. The Ranger's Natural Explorer feature grants advantage on foraging checks and doubles the amount of food they find when successful (letting them cover for one additional person, or three when combined with the Outlander feature). If someone is casting Goodberry or similar each day, it is assumed they cast it at dusk for the sake of spell slots during random encounters.

Day-by-Day Rules

A day is broken down into six parts, three for travel (morning, afternoon, and evening) and three for making camp (dusk, midnight, and predawn). Each day there is a chance for a discovery, and each section of the day there is a chance for a random encounter, the chances for both of which are determined by the area.  
At the beginning of the day, the party sets their travel pace, each party member makes a foraging check, and the navigator makes a navigation check.
Each party member who fails their foraging check marks off a pound of rations, though everybody finds water as long as at least one person succeeds. The Outlander background's Wanderer feature grants a +2 to foraging checks and allows them to forage enough food for an additional person when successful. The Ranger's Natural Explorer feature grants advantage on foraging checks and doubles the amount of food they find when successful (letting them cover for one additional person, or three when combined with the Outlander feature).
The navigation check is rolled by the DM behind the screen, and if this check fails the party becomes lost. The party makes no progress while lost, and will not discover that they are lost until the navigator succeeds another daily navigation check. To become un-lost, the party must describe how they reorient themselves, such as backtracking along their own trail or following a river. The Outlander background's Wanderer feature grants a +2 to navigation checks, and the Ranger's Natural Explorer feature grants advantage.

Travel Time

Base travel time (per 24 miles) depends on the terrain:

• 1 day for trivial terrain (farmland or roads)

• 2 days for easy terrain (plains, desert, etc.)

• 3 days for rough terrain (forests, marshes, etc.)

• 4 days for treacherous terrain (mountains, swamps, etc.)

Pace

• A slow pace covers 2/3's the normal amount of ground per day, but allows for foraging and provides advantage on travel-related skill checks.

• A normal pace is, well, normal; foraging is at disadvantage, but skill checks are normal.

• A fast pace covers 1 1/3's the normal amount of ground per day, but foraging is impossible and travel-related skill checks are at disadvantage.

Mounts

Some mounts cannot handle difficult terrain, and most mounts cannot handle treacherous terrain - they can, for the most part, be walked through these areas rather than left behind, but travel there will have to be on foot.

• Slow pace = normal pace on foot

• Normal pace = 1 1/3's worth of ground per day (fast pace on foot)

• Fast pace = 1 2/3's worth of ground per day