Hi HH8. I took those in May, though the wildflowers remained blooming until early July in that particular location. For some reason they start late and last longer over towards the Mission Creek drainage.
If you want to see great wildflowers, start at the Whitewater preserve and go south. March or April will be best, and after a good rain year it is unbelievable. There are red, purple, blue, yellow, and white flowers in such profusion that it's absolutely amazing. In drier years the grassy hills are still pretty with occasional bursts of yellow flowers.
If you'd like an astounding view of San J, if you can find your way to the saddle that stands between Whitewater and the Cottonwood trailhead for the PCT, just go west up the ridgeline from the saddle. It looks like you're in an airplane and San J is snowcovered that time of year, so it's spectacular in person.
Here's a link for some pics from there:
http://outdoors.webshots.com/album/570543088WZVuRM
Sort of like the Grand Canyon in that the pics can't do it justice. Fairly short hike too from either direction, maybe 3-4 miles from either end, then a 1/2 mile scramble/stroll up the ridgeline. Let me know if you have a chance to go in the spring. I do a lot of runs out there when the mountains are too cold for a quick run and I'll let you know if the flowers are in bloom yet. Root for a great rain/snow year!
z