Grinding Rock park, not far from Jackson, California, is one of the most comprehensive Native American sites in the US, dedicated to an understanding of the Miwok people who once lived there. Tools, basketry, replica ceremonial dwellings and a superb collection of rock carvings were all interesting but the highlight was undoubtedly the 1,000-plus, lunar-like “mortar holes” in the limestone rocks. Made by generations of Miwok as they ground acorns to make meal, they provide a rare and indestructible imprint of an ancient way of life. Fascinating – and we had the site almost to ourselves. There are also mile-long trails and plenty of wildlife in the surrounding oak and pine woods.