Echinocereus sciurus is one of the hedgehog cacti. It is native to a small area at the very tip of Baja California del Sur, Mexico. Because it grows trailing over the rocks, its Latin species name is "squirrel tail." Echino = spiny, cereus = candle. It is not common in cultivation. I got this as a 1"/2.5cm tall seedling many years ago. It is growing in a 6"/15cm pot and the flowers are about 3.5"/9cm across.
There are a few species of Echinocereus in Baja California, most of which flower in spring or summer. Other species of Echinocereus occur from the far northern plains of the US, and down through the southern deserts of Mexico. They are typically easy to grow. Many have very impressive flowers. Several are hardy outdoors in winter in most of the US and Europe if protected from most winter wetness.
Those interested in trying them outside should look into E. pulchellus, triglochidiatus, and viridiflorus, which has many varieties previously considered species. Of these E. pulchellus is the least hardy, but is well suited to life in a 3" / 7.5cm pot: it is solitary, stays very small, and makes a lot of flowers. It needs dappled light, since it is small, and typically grows in grassland.
E. triglochidiatus is a large to very large plant. It is from high elevations in Arizona, New Mexico, Colorado and Utah, and tolerates very cold overnight snaps if completely dry. It may not flower well in areas with cloudy winters.
E. viridiflorus is the hardiest to cold and wet winters, naturally occurring into Wyoming. Its different subspecies make tiny to small, clustering or solitary, stems. Many types have mature stems the size of a fingertip that soon form tight clumps of dozens of heads. Its profuse, small, very early spring flowers are brown to bright yellow to green in different populations, and most have a very strong lemony scent. It typically flowers at the beginning of snowmelt, and flowers are rarely damaged by frost. Spine color can vary from white to red to black, and various combinations; from very short and neat, to longer and shaggy. Those of you with cold winters should try a viridiflorus in your garden, in a gravelly raised area that gets as much winter sun as possible.