NPS/Jane Cipra

Figure 1. Eureka Dunes, Death Valley National Park.

Eureka Valley in Death Valley National Park, California, contains a dune system between 900 and 1,300 meters (2,953–4,265 ft) in elevation that is split into three dune areas: the Main Dune, the Saline Spur, and Marble Canyon (fig. 1, above, and fig. 2). This dune complex is the entire range of two endemic species: the Eureka Valley dune grass (Swallenia alexandrae [Swallen]) and the Eureka Valley evening primrose (Oenothera californica ssp. eurekensis [Munz & Roos]), which are both federally listed as endangered species (43 FR 17910-17916, 26 April 1978).

Swallenia alexandrae is a perennial grass that forms stable hummocks approximately 1–3 m in diameter (3–10 ft), found primarily on the mobile sand that forms the steep slopes of the dunes (Pavlik 1979). The grass stems ascend up to 1 m high and are often branched. Although drifts of sand frequently bury Swallenia hummocks, giving the branching stems the appearance of multiple individuals emerging from the sand, Swallenia does not reproduce asexually through true rhizomes or stolons (Pavlik and Barbour 1985). Instead, Swallenia reproduction occurs solely by seed and appears to be dependent on warm-season rains in late summer and early fall (Pavlik and Barbour 1988).

Oenothera californica ssp. eurekensis is an herbacious perennial primrose that dies back to the roots and remains dormant in the subsurface in dry years. This subspecies of Oenothera differs from others in that it is capable of forming new vegetative rosettes at the ends of buried branches (Pavlik 1979). Oenothera also reproduces by seed and is pollinated by hawkmoths (Hyles lineata) (Gregory 1963).

Because of the popularity of the Eureka Valley for off-road vehicle (ORV) recreation in the 1970s, O. californica ssp. eurekensis and S. alexandrae were both listed as endangered species in 1978, with ORV recreation cited as the threat to their populations. The Eureka Dunes were officially closed to ORV use by the Bureau of Land Management (BLM) in 1976 when Swallenia and Oenothera were proposed for listing (Noell 1994); however, enforcement of this closure was not fully implemented until 1980 (USFWS 1982). Occasional ORV trespass still occurs at the Main Dune (Death Valley National Park patrol logs).