Surprisingly very few of our LA friends/colleagues have ever been to Joshua Tree. It’s one of the nation’s newest national parks, so perhaps it is still somewhat undiscovered.
We recommend going during a warm winter weekend because the desert heat probably will be brutal when it gets warmer. Keep in mind that it’s the desert so it’s very dry out there. Bring lotion for dry skin and lots of water. Even though it was a cool day (high 60s, low 70s), we were surprised at how much water we were drinking to keep from getting parched.
One thing we did not fully appreciate before we went there was that the area is great for rock climbing and bouldering. We wished we were better prepared and allotted more time for rock climbing.
If you are ever going out to Palm Springs for a weekend or holiday, I highly recommend to spend one full day at Joshua Tree. Get up early and spend the morning bouldering or rock climbing before it gets too warm. The main sites/attractions (including the odd-looking Joshua Trees themselves) are driveable and/or accessible on short hikes, so save them for the afternoon.