There is some confusion on what to call this flower:
Turner and Gutafson call it A. amplexicaulis (p273).
USDA lists both A. lanceolata (AK; New England) and A. amplexicaulis (western NA) with no varieties.
H&C lists A. amplexicaulis with two varieties:
var. piperi: leaves are very wide >4 cm
var. amplexacaulis: leaves are < 4 cm and widely found.
eFlora lists A. lanceolata with two subspecies:
ssp. lanceolata (eastern NA)
ssp. prima (western NA)
ITIS states that A. amplexicaulis is now called A. lanceolata with eFlora's two subspecies.
both species were called Clasping Arnica.
Based on ITIS and WTU I am calling these flowers A. lanceolata ssp. prima
Note leaves are toothed, clasping in opposite pairs. End of petals are somewhat straight across and generally have three teeth. Found in wet areas.
west Central Cascades; west Olympics, west North Cascades
TRAIL: Mt Sawyer; Heart Lake; Goat Mtn.
HABITAT: subalpine meadow (wet); Open hillside;
ELEVATION: 1,170 - 1,990 m (3,840 - 6,525 ft.)
BLOOM TIME: 15-JUL 22-AUG 03-AUG