Thirty years ago, Philippa Drennan joined her colleague John Waggoner in a study of Joshua trees in the Mojave Desert. His initial research that concerned the distribution of Joshua trees within a range of altitudes in the remote desert became long-term monitoring of new growth and flowering of specific trees. Changes in climate and environment have affected the trees, and Drennan describes here what they have observed through their research in the Mojave National Preserve.