This is a very small population of a rare flower. The property owners are working on improving the size of the marshland to allow for a greater size of population of this plant. The only other populations are located a bit north in Knights Valley. I am going to try to find them next.
Possible herbarium specimen
Sidalcea is a genus of the botanical family Malvaceae. It contains several species of flower known generally as checkerblooms or checkermallows, or prairie mallows in the United Kingdom. They can be annuals or perennials, some rhizomatous. They are native to West and Central North America.