Authorities said the two men were on a morning bike ride in the foothills near North Bend when the attack occurred. The town is about 30 miles (48 kilometers) east of Seattle.
The mountain lion ran into the woods and officers with the Washington Department of Fish and Game later tracked it down and shot and killed it, said Capt. Alan Myers of the state's Fish & Wildlife Police.
The 31-year-old survivor was taken to a hospital in Seattle. He was initially listed in serious condition in the emergency room but was alert and talking; his condition was later upgraded to satisfactory, The Seattle Times reported.
A search and rescue team was dispatched to recover the body of the deceased man.
KIRO-TV reported that the injured man called 911 shortly before 11 a.m. and shouted, "Can you hear me? Help!" and then the call hung up.
Authorities found the cougar standing over the body of the dead biker, the station reported.
It wasn't immediately clear if the two victims were biking together or separately.
In the last 100 years in North America, roughly 25 fatalities and 95 nonfatal cougar attacks have been reported, the Washington Department of Fish & Wildlife said, but there was only one other fatal attack in the state. However, more attacks have been reported in the western United States and Canada over the past 20 years than in the previous 80 years.
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