Ethiopia's Cenozoic flood basalt magmatism, uplift, and rifting have been attributed to one or more mantle plumes. The Nubian plate, however, has drifted 500\add[A.B.]{--1000},km north since initial magmatism at $\sim$45Ma,havingdevelopedabovemantlethatnowunderliesthenorthernTanzaniacratonandthelow-lyingTurkanaDepression.Unfortunately,ourknowledgeofmantlewavespeedstructureandmantletransitionzone(MTZ)topographybelowtheseregionsispoorest,duetoahistoricallackofseismographstations.ThesamedatagapmeanswelackconstraintsonlithosphericstructureinandaroundtheNW--SEtrendingMesozoicAnzarift.WeexploitdatafromnewseismographnetworksintheTurkanaDepressionandneighboringnorthernUgandatodevelopAFRP22,anewAfricanabsoluteP-wavespeedtomographicmodelthatresolveswholemantlestructurealongtheentireEastAfricanriftsystem.WealsomapMTZthicknessusingPsreceiverfunctions.EastAfrica\prime sthinnestMTZ($\sim$25,km thinning) underlies the northwest Turkana Depression. AFRP22 reveals a co-located, previously-unrecognized, slow wavespeed plume tail, extending from the MTZ, deep into the lower mantle. This plume may thus have contributed, along with the African Superplume, to the development of the 45--30,Ma flood basalt province that preceded extension. Pervasive sub-lithospheric slow wavespeeds imply that Turkana's present-day low elevation is explained best by Mesozoic and Cenozoic-age crustal thinning. At $\sim$100,km depth, AFRP22 illuminates a fast wavespeed SE Ethiopian plateau. In addition to governing the northernmost limit of Mesozoic Anza rifting, the refractory nature of this lithospheric block likely minimized Cenozoic flood basalt magmatism there.