(CNN) Curtis Whitson has two strangers to thank for his family being alive today. Two brave hikers plucked a lime green bottle from a river and alerted authorities about the SOS message they found inside.

Whitson, his 13-year-old son and girlfriend, Krystal Ramirez, had decided to spend Father's Day weekend backpacking the Arroyo Seco River.

They spent their days boulder-hopping and floating the river on inner tubes, and their nights sleeping under the stars, bundled in lightweight mummy bags, with mesh bags over their heads to keep bugs at bay.

Whitson was in familiar territory: he takes as many as 20 backpacking trips to the central California coastal forest each summer.

Throughout the trip, the family's goal was to reach the Arroyo Seco narrows, float through the water shoot and down the waterfall before joining friends to float the last couple of miles down to a campground. After two and half days of lugging 50-pound packs, the family reached the narrows, a spot in the river surrounded by solid rock up to 40 feet high on each side.

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