The weather, honestly.

If you have not been to a desert in winter, you should come between November and March. Daytime in the mid-70s, nights cold enough for a fire pit and a jacket, and the sky as dark as it gets all year.

• January. Highs 68°F · Lows 42°F. Quietest month in town. Clear, cold, ideal for hiking.
• February. Highs 72°F · Lows 45°F. Wildflowers begin late month in a good year.
• March. Highs 78°F · Lows 50°F. Peak wildflower season. Book early — this is our busiest month.
• April. Highs 86°F · Lows 56°F. Last truly comfortable hiking weather. Wildflowers wind down.
• May. Highs 95°F · Lows 64°F. Shoulder season — pool weather, still cool nights.
• June. Highs 104°F · Lows 72°F. Summer begins. Milky Way core rises before midnight.
• July. Highs 107°F · Lows 78°F. Monsoon thunderstorm season. Dramatic skies.
• August. Highs 105°F · Lows 77°F. Perseid meteor shower under the darkest skies in California.
• September. Highs 100°F · Lows 71°F. Heat softens. Crowds disappear.
• October. Highs 88°F · Lows 60°F. The desert exhales. One of the best months overall.
• November. Highs 76°F · Lows 50°F. Peak fall — sweater nights, warm afternoons.
• December. Highs 68°F · Lows 42°F. Longest nights of the year. Geminid meteors mid-month.

Always: sunscreen, a wide-brim hat, a refillable water bottle. November–April: a warm puffy for after sunset. May–October: swimwear and a strategy for the heat (most days, that strategy is "pool by 11am, AC by 1pm").