▁part ▁of ▁the ▁Ba etic ▁System ▁in ▁the ▁Cam po ▁de ▁Gib ral tar . ▁The ▁local ▁rocks ▁are ▁mainly ▁composed ▁of ▁fly sch ▁compr ising ▁mar l , ▁sand stone ▁and ▁m ica , ▁locally ▁known ▁as ▁the ▁Al ger icas ▁Fly sch , ▁that ▁dates ▁from ▁the ▁E oc ene – O lig oc ene ▁period . ▁The ▁rocks ▁include ▁various ▁soft ▁min er als , ▁especially ▁cl ays , ▁mar l , ▁cal car en ite ▁and ▁sand st ones , ▁that ▁have ▁er oded ▁to ▁leave ▁behind ▁the ▁harder ▁lim est ones ▁and ▁thus ▁form ▁the ▁chain ▁of ▁alternate ▁cov es ▁at ▁C ala ▁Ar enas . ▁ ▁Several ▁notable ▁arch ae ological ▁sites ▁are ▁located ▁near ▁C ala ▁Ar enas . ▁The ▁area ▁has ▁been ▁inhab ited ▁for ▁thousands ▁of ▁years , ▁the ▁result ▁of ▁its ▁strateg ic ▁position ▁in ▁the ▁Stra it ▁of ▁Gib ral tar ▁and ▁the ▁easy ▁landing ▁place ▁that ▁it ▁has ▁represented ▁histor ically . ▁A ▁small ▁Pho en ician ▁port ▁existed ▁there , ▁probably ▁with ▁a ▁watch t ower . ▁A ▁medieval ▁def ensive ▁structure ▁called ▁the ▁Rec into ▁del ▁Cer ro ▁de ▁la ▁Hor ca ▁stood ▁nearby , ▁as ▁did ▁a ▁ 1 6 th - century ▁watch t ower , ▁the ▁Torre ▁del ▁Fra ile . ▁The ▁ 1 8 th ▁century ▁F uerte ▁de ▁San ▁Diego ▁was ▁also ▁situated ▁in ▁the ▁area ▁but ▁was ▁destroyed ▁in ▁ 1 8 1 1 ▁by ▁British ▁troops ▁from ▁Gib ral tar , ▁who