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One video shows the mating behavior of many males around a female that emerged recently, and the other videos show some of the male activity over the nesting area as they search for emerging females. It's hard to capture how many bees were active and how impressive of their activity is in both sight and sound, but these videos give a limited sense of it, although you'll have to imagine the immersive buzz the bees made all around me unless/until I can extract audio to upload as a sound file. (By the way, the slight motion of the background relative to the foreground in the videos is an artifact of processing used stabilize the hand-held video so it doesn't jump around.)

The still photos show new nests (indicated by the fresh sand piles) being dug by females that have already emerged and mated. Over the past few days, the number of new nests went from a few to dozens in several nesting areas I've observed throughout this area; nearly all of the nests in the last two photos were new since I searched that sand ridge a few days ago.

Here's an approximate timeline of activity for these bees based on my observations:

Around March 15, the first males became active. They were common and active around the flowering manzanitas and huckleberries; it looked like they were patrolling for females as well as occasionally feeding at the flowers (e.g., this observation).

About 10 days later, around March 26, males were actively patrolling nesting sites in the sand, although no new nest burrows were present yet. The first females became active and the first mating took place (e.g., this observation).

About a week later, around April 3, males became abundant and highly active around nesting areas, while some males still patrolled flowering plants (in this area still mainly manzanita and huckbleberry plants), and additional females became active along with more mating. The first large mating aggregations became obvious. New nest burrows were still rare (e.g., this observation and this observation).

Within days (by April 5), females that had mated were digging many new nest burrows (e.g., this observation and today's observation above).

For now, activity continues whenever rain stops, clouds thin, and temperatures reach the high 40s to mid 50s F.

This is a male bee, measuring 10.5 mm, found feeding on resinbush (Viguiera stenoloba). Identified from specimen by John L. Neff. Coelioxys (Rhinocoelioxys) zapoteca is a subtropical bee. Its occurrence At Falcon SP (Starr County) marks a range extension; previously, the species’ northern range was thought to be the state of San Luis Potosi. [A description of this species can be found in: Filho, Léo Correia Da Rocha, and Packer, Laurence (2015). Revision of the neotropical subgenera Coelioxys (Platycoelioxys) Mitchell and C. (Rhinocoelioxys) Mitchell (Hymenoptera; Megachilidae) with the description of one new species. Zootaxa 3941 (2): 151-203.]

Tumamoc Hill, The Desert Laboratory, The University of Arizona, Tucson, AZ.

Historically, the eastern creosote bush flats (between two washes) has been rather consistently the nesting aggregation and emergence sites of Centris pallida for decades.

I saw metanders (large male morphs) at this site again on May 10, 2023 searching for micro sites to dig for females. However, this was not a good year. Some years, this area (perhaps 10 hectares) contains many thousands, even tens of thousands, of searching and patrolling males, mating pairs and nesting females.
Meghan Barrett conducted some of her C. pallida thermal biology Ph.D. studies (Drexel Univ.) here in 2018 and 2019. Buchmann has also worked onsite with cinematographer Keith Brush to film mating behavior, and with still photographer Dr. Bruce Taubert.

Historical (recent) bee emergence dates at this TH site have been:
14 April - 8 May 2016
24 April - 4 May, 2018
13 April - 29 April, 2019

Climate change:
Interestingly, Centris pallida emergence dates (Tumamoc Hill, Blue Pt. Bridge recreation area along the Salt River) in the 1970's and 1980's were strongly at the tail end of April, or early May. Today, we expect to see these bees emerging about 10 days earlier.

*Note- photographs of Centris pallida adults and brood cell courtesy of Dr. Bruce Taubert. Please DO NOT reuse without permission.

This is a wild-ass guess—these look more like wasps than bees to my eye—but these are beautiful insects.

Hoping that tagging a genus will help the right folks see this (and either reclassify correctly or narrow down further).