T-Mobile, which tends to have weaker rural coverage than either AT&T Mobility or Verizon Wireless, nevertheless appears to have strong coverage around the Empire Polo grounds on 51st and Monroe. Maybe that's not surprising given that T-Mobile's target demographic is the youngest among the four mobile providers. For Sprint, our model suggests there is no service in the area of the concert venue, but we encourage concert-goers who have Sprint to download CalSPEED (free download from iTunes or Google Play) and run some tests for us, because those test results will help us improve our model. The one CalSPEED test we have from crowdsourcing for Sprint in downtown Coachella shows no service, but a field test location near Harrison and Airport Boulevard shows over 7 Mbps down and over 4 Mbps up.
Here are images showing the interpolated mean minus two standard deviation downstream speeds for each provider for the area around Coachella. Concert venue is indicated by a star.
T-Mobile: 3.0-6.0 Mbps downstream
Verizon Wireless: 3.0-6.0 Mbps downstream
AT&T Mobility: 1.5-3.0 Mbps downstream
Sprint: No service