## 3 Material and Methods  
We collected 195 samples along a vertical profile in the Gran Dolina cave in plastic bags using non-magnetic instruments. Due to the current state of the archaeological site, we logged and sampled two complementary different profiles: one comprising units TD6-TD8.9 and another about 5 m to the SE for the units TD9-TD10 (as shown in Figure 1b,c). Our rockmagnetic study was carried out in both the Archaeomagnetism Laboratory at the CENIEH (Burgos, Spain) and Paleomagnetism Laboratory at the University Complutense of Madrid (UCM). The following measurements were performed at CENIEH: susceptibility at two frequencies, isothermal and anhysteretic remanent magnetization, and hysteresis loops. The thermomagnetic study was carried out at UCM. The bulk susceptibility was measured with an Agico MFK1-FA instrument, obtaining in addition the phase angle--a parameter influenced by all the mineral fractions present in the samples [32] and defined as the difference between in-phase and out-of-phase susceptibility [33; 34]. The same instrument was used to measure the susceptibility at two different frequencies, \(\chi_{lf}\) and \(\chi_{hf}\), 976 and 15.616 Hz, respectively. We then normalized the frequency-dependent susceptibility (as suggested by [35]) as follows:  
\[\chi_{fn}=\frac{\chi_{fd}}{\ln\chi_{hf}-\ln\chi_{lf}} \tag{1}\]  
where \(\chi_{fd}=100\left(\chi_{lf}-\chi_{hf}\right)/\chi_{lf}(\%)\)--as introduced by [36]--\(\chi_{hf}\) and \(\chi_{lf}\) are the high and low frequencies, respectively. We measured the hysteresis cycles with a MicroMag 3900 VSM (Vibrating Sample Magnetometer, LakeShore instrument, MIT Lincoln Laboratory, Cambridge, MA, USA), which is capable of reaching a maximum field of 1.3 Tesla, although we use 0.5 T. The samples used for this instrument were prepared in small gel capsules of \(\sim\)0.10 mL volume. Remanence (IRM, ARM) was measured with a three-axes SQUID cryogenic magnetometer (SRM, 2G Enterprises, Applied Physics Systems, Silicon Valley, CA, USA). Additional progressive IRM acquisition curves up to 5 T were obtained by an impulse magnetizer (ASC Scientific, Model IM10-30, Narragansett, RI, USA), which were used to infer the magnetic components present through their magnetic coercivity. In order to determine the relative concentration of low to high coercivity minerals, we carried out a particular study based on the application of a saturation magnetization (SIRM) of 5 T, with the help of the impulse magnetizer, followed by alternating field demagnetization at 100 mT to remove the contribution of any ferrimagnetic minerals (e.g., magnetite). Next, we set thermal demagnetization at 130 \({}^{\circ}\)C to remove the goethite contribution (method described by [37]). The grain size and mineralogical composition are inferred from several ratios: the parameter S-ratio provides a measure of the relative amount of high-coercivity to low-coercivity remanence and is obtained by dividing the backwards remanence at 0.3 T with the isothermal remanent magnetization at 1 T. In addition, the ARM/IRM\({}_{\rm 1T}\) and IRM\({}_{\rm 1T}\)/X\({}_{\rm 1f}\) ratios were also used. The thermomagnetic curves were obtained at the Paleomagnetism Laboratory at UCM by AGICO KLY-4S Kappabridge coupled with the CS-3 Temperature Control Unit, able to measure the low-field susceptibility variation in the range from ambient temperature to 700 \({}^{\circ}\)C.  
Lastly, we use the traditional Day plot, which compares the M\({}_{\rm rs}\)/M\({}_{\rm s}\) with H\({}_{\rm cr}\)/H\({}_{\rm c}\) ratio and provides information about the domain state of the iron oxides, as well as the King plot to determine the grain size on the basis of the slope given by comparing the ARM susceptibility versus the low-field susceptibility. For a better comprehension of the manuscript, we include in Table 1 all acronyms used, and in Table 2 we include the used parameters-plot with their interpretation.