The Presidio of Tucson is dated back 4,000 years, but is officially said to have originated Aug. 20, 1775. That makes this year Tucson's 240th birthday and Tohono Chul, 7366 N. Paseo del Norte, is throwing an educational celebration Saturday, Aug. 15. From 9 to 10 a.m., the park will host a presentation by local historian Ken Scoville, who will give an in-depth lecture chronicling the city's evolution from a small Spanish presidio to the thriving city we now call home. Admission is $10 for the general public and $6 for members. For more info, visit www.tohonochulpark.org.