California’s record of this jumping mouse is a coast-hugging thing. All 42 reports since 2000, every one from iNaturalist observers, fall in four coastal counties, and Humboldt County holds 30 of them, with Redwood National Park accounting for 12 records inside that cluster. Marin County adds 4 from the Point Reyes peninsula, and Del Norte and Mendocino fill in the edges. Nothing in the record reaches inland past the fog belt.
That pattern fits the animal. Jumping mice need damp ground and thick streamside cover, and the redwood coast delivers both in a way the dry interior doesn’t. Reports build through spring and crest from July to September, when the mice are most active before their long hibernation, which can stretch half the year. The total is still small, and NatureServe hasn’t ranked the species at either the state or global level, so nobody should read the Humboldt cluster as proof of abundance there. It mostly shows where coastal naturalists with sharp eyes have been looking.
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