We report on measurements of the resistivity and Hall coefficient in underdoped GdBa2Cu3O7-delta epitaxial thin films grown by off-axis magnetron sputtering. The films have been lithographically patterned allowing precise measurements of the temperature dependencies of the inverse Hall constant R-H(-1) and of the Hall angle theta (H). We find that R-H(-1) is linear in temperature between 300 K and the pseudogap temperature T*, whereas cot(theta (H)) displays a perfect T-2 temperature dependence typically between 300 and 100 K. We observe for all the samples that the temperature at which the temperature dependence of cot(theta (H)) deviates from the T-2 behavior is correlated to the temperature at which R-H displays a peak. This characteristic temperature, found to lie between T-c and T*, does not depend markedly on the doping level and defines a crossover line in the temperature versus doping phase diagram. We tentatively relate these findings to recent high-frequency conductivity and Nernst effect experimental results, and we briefly discuss the possible consequences fur competing theories fur the pseudogap state of the cuprates.