Trillium chloropetalum or T. kurabayashii—we don't know which trillium this is for sure. For anyone interested in trilliums, the book to get is Trilliums, by Frederick W. Case, Jr. and Roberta B. Case, published by Timber Press which has excellent photographs and descriptions of the myriad species and hybrids. Even if you don't know the species name, enjoy and collect them!