Her sons were alive.

The Walla Walla people sheltered them.

Franchère’s brigade recognized them in the spring.

The space between the decision to flee west and the arrival at the Columbia River is the essential mystery of Marie Dorion’s story.

It is a mystery not because it cannot be understood in principle — the basic requirements of winter survival in that terrain are knowable — but because the documentary record does not preserve the specific details of how she met those requirements.

What it preserves is the outcome.