A few months after Emmilee Risling went missing, her parents received a map.

It was crudely drawn, sketched in ink on lined notebook paper. Slashed lines indicated roads; a rectangle marked a fire station.

An acquaintance had passed it along from an anonymous tipster who had a chilling message: Their daughter was buried there, under a rock.

Ms. Risling, 32, had disappeared on the Yurok Reservation, which stretches like a jagged scar across Humboldt and Del Norte Counties in Northern California. At nearly 56,000 acres, the land is about twice the size of San Francisco, much of it layered in dense, hilly forests of redwood, fir, madrone and tanoak.

The landscape is majestic as it follows the Klamath River, but its rugged topography can feel impenetrable. The main roads are few and far between, winding through thickets of evergreen that, even when broken with sunlight, are deep and secretive. Cell service is either spotty or nonexistent.

Ms. Risling had taken to hitchhiking after her car was stolen. Among the last places she was seen was Pecwan Bridge, which stretches over a creek near the Klamath. Residents also reported that she had been a mile north of there, in an isolated area where the main thoroughfare fades and the river shimmers below. It is known as End of Road.

Family members wanted a search conducted immediately after her disappearance in October 2021, but the Yurok Tribal Police comprised only five officers and two command staff. They were not trained in search-and-rescue operations.