The GaAs/AlGaAs quantum well (QW) system is utilized to investigate the electron spin relaxation in the satellite X valley of indirect band gap epitaxial layers through polarization-resolved photoluminescence (PL) excitation spectroscopy. Solving the rate equations, steady-state electronic distribution in various valleys of is estimated against continuous photocarrier generation, and an expression for the degree of circular polarization (DCP) of PL coming from the adjacent QW is derived. Amalgamating the experimental results with analytical expressions, the X-valley electron spin relaxation time is determined to be 2.7 ± 0.1 ps at 10 K. To crosscheck its validity, theoretical calculations are performed based on density functional theory within the framework of the projector augmented wave method which support the experimental result quite well. Further, temperature dependence of is studied over 10–80 K range, which is explained by considering the intravalley scattering of carriers and Dyakonov-Perel spin relaxation in the X valley of the indirect band gap AlGaAs barrier layer. It is learned that the strain-induced modification of band structure lifts the degeneracy in the X valley, which dominates the electron spin relaxation . Furthermore, the DCP spectra of hot electrons in indirect band gap AlGaAs layers are found to be significantly different than that of direct bandgap AlGaAs. It is understood as a signature of linear -dependent Dresselhaus spin splitting and the faster energy relaxation procedure in the X valley.