J. multifida lacks the serrated edge, but you may be on to something. It does bear some minor resemblance to the Cannibaceae, except the leaves of cannabis and hops and the like are fuzzier and have more parallel veins and lobes; the serration isn't right either. It almost looks like the foliage of J. paradoxa, but given rattler's location I have doubts. How many Jatropha range into Montana? I mean, I can see it happening given the distribution of the genus, but only a few oddballs at best.
After looking a little more, it kind of looks like my J. gossypifolia, except the leaves aren't the right color quite. Are the joints of the petioles and nodes surrounded by small glands? They look kind of like Drosera tentacles, superficially, and sometimes secrete sap.
~Joe