Russell Chatham was an American landscape artist based for most of his career in Montana. Though he also produced oil paintings, he is known in particular for his beautifully subtle color lithographs, some of which use 30 or more layers of color to attain the final image.
His work shares some characteristics with tonalist painting, but I think of it as something aside and quite unique. I love the soft, poetic nuances of his color and value relationships, the meditative stillness of his scenes and the often bold geometry of his compositions.
Russell Chatham died this past November, 2019, at the age of 80. I don’t know of a dedicated website for his work; I’ve linked to a few other sources that I could find.