The temperature dependence of the EPR fine structure linewidths of (0.01 Gd, 0.99 Eu) (OH)3 monocrystals has been measured to study the dynamic interactions in this lattice. It is inferred from the complex behavior that static strain is the dominant linewidth broadening mechanism if T<85 K and that dynamic magnetic interactions dominate if 85 K<T. An abrupt change in the linewidth ratios observed between 100 and 115 K cannot be explained by the above mechanisms. It is suggested that a structural change may occur near 115 K. X-ray diffraction structural data supports this proposal. However, the temperature accuracy of these latter measurements is insufficient to be definitive. It appears that the rate at which a-dimension of the unit cell contracts changes at about 115 K and represents a transition from an easy to a hard mode of contraction.