A group of 6-8 medium sized animals were flying in the desert sunset. The animals were colored between ranges of colors, gray, black and brown, they made very high-pitched noises and by the way they flew they can be identified as bats. These mammals were probably looking for nectar.
One photo seems to suggest it's a hoary bat.
One individual observed. It looked through my 100mm T5.6 lens that it was bigger than the other bats I've observed. It repeated what I imagine were it's feeding flights. It was using the airspace above a drainage area of the grassy/blue oak hillside slope. I was under eye level with it. It was 20-100 feet above my eye view. Nearby were the palisade rocky cliffs of Rockville Hills Park which look like they afford many cracks and crevices that would attract roosting and migrating bats. Also nearby were several shallow reservoirs. From the photo sequence it appears the bat flew near me and then flew to higher air and further away from where I stood.
Also included are tree photos show landscape below and to the side where the bat was seen flying.