There are the Cardenas Basalts of the Grand Canyon Supergroup at the bottom of Grand Canyon and the Uinkaret plateau lava flows which are much higher up.
Rb/Sr radioisotope measurements were made of these rocks. The Uinkaret lava flows were measure and computed to be ~1.3 Billion years old while the lower Cardenas Basalts were measure and computed to be ~1.0 Billion years old.
Anomaly?