The Death Valley National Park is the lowest, the dryest and the hottest place in the United States. In 1913 the temperature of 56°C was recorded here, still an unsurpassed world record. However, during autumn this area gets occasionally flooded after severe rainstorms. And water abundance in such a dry place results in an interesting phenomenon, which is called the super bloom. The following spring the Death Valley becomes covered with thousands of wildflowers, attracting a few hundred thousand visitors during one season.
The desert gets filled with a sea of yellow, blue and white flowers. You can see sunflowers, phacelia, desert gold, gravel ghost, Bigelow monkeyflower, desert thorn, desert sage, poppies and other plants that are able to survive in such a harsh climate. Remember that super bloom is a rare event that occurs only after substantial rainfall in the autumn and winter. But it was observed in 2005 and 2016, so if you get lucky, you can see it too. Keep an eye for the updates.
Even without the super bloom, you have good chances to witness a decent number of wildflowers in the Death Valley National Park. The best time to visit is from late February through April. At this time, you can spot flowers on lower elevations. Check out Badwater Road, Green Valley Road, Death Valley Road, and Titus Canyon Road. Starting from mid-March, flowers appear on higher elevations: check out Jubilee Pass, Zabriskie Point, Furnace Creek, and Daylight Pass. In May, there is a good chance to spot the flowers in the Panamint Range area.