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四(si)川盆地(di)聚居(ju)著四(si)川省和(he)重慶市大(da)部(bu)分人(ren)口(kou)、居(ju)民主要為漢族巴蜀民系。是中國和(he)世(shi)界上(shang)人(ren)口(kou)最多(duo)的區(qu)域之(zhi)一。
中(zhong)(zhong)國著(zhu)名紅層(ceng)盆(pen)(pen)地(di)，中(zhong)(zhong)國各大(da)盆(pen)(pen)地(di)中(zhong)(zhong)形(xing)態最(zui)典(dian)型、緯度最(zui)南、海(hai)拔最(zui)低的盆(pen)(pen)地(di)。位(wei)于長江上游地(di)區，海(hai)拔500米左右，長江把它(ta)和東(dong)海(hai)一(yi)脈相連，它(ta)是中(zhong)(zhong)國最(zui)大(da)的外(wai)流盆(pen)(pen)地(di)。
四川(chuan)(chuan)盆(pen)(pen)地(di)(di)(di)(di)的(de)(de)(de)(de)面(mian)(mian)積約26萬余(yu)平(ping)方(fang)(fang)千米(mi)（面(mian)(mian)積是(shi)居第五第六位的(de)(de)(de)(de)兩(liang)湖盆(pen)(pen)地(di)(di)(di)(di)和(he)(he)銀額盆(pen)(pen)地(di)(di)(di)(di)的(de)(de)(de)(de)兩(liang)倍），占四川(chuan)(chuan)省(sheng)面(mian)(mian)積的(de)(de)(de)(de)46%。四川(chuan)(chuan)盆(pen)(pen)地(di)(di)(di)(di)西(xi)(xi)依(yi)青(qing)藏高原(yuan)(yuan)和(he)(he)橫(heng)斷山(shan)(shan)脈(mo)，北近秦巴山(shan)(shan)脈(mo)，與漢中盆(pen)(pen)地(di)(di)(di)(di)相望，東(dong)接湘鄂西(xi)(xi)山(shan)(shan)地(di)(di)(di)(di)，南(nan)連云貴高原(yuan)(yuan)，盆(pen)(pen)地(di)(di)(di)(di)北緣(yuan)米(mi)倉山(shan)(shan)，南(nan)緣(yuan)大(da)婁山(shan)(shan)，東(dong)緣(yuan)巫山(shan)(shan)，西(xi)(xi)緣(yuan)邛崍山(shan)(shan)，西(xi)(xi)北邊(bian)緣(yuan)龍(long)(long)門(men)山(shan)(shan)，東(dong)北邊(bian)緣(yuan)大(da)巴山(shan)(shan)，西(xi)(xi)南(nan)邊(bian)緣(yuan)大(da)涼山(shan)(shan)，東(dong)南(nan)邊(bian)緣(yuan)相望于武陵(ling)山(shan)(shan)。這(zhe)里的(de)(de)(de)(de)巖(yan)(yan)石，主要(yao)由紫紅色(se)(se)砂巖(yan)(yan)和(he)(he)頁巖(yan)(yan)組(zu)成(cheng)(cheng)。這(zhe)兩(liang)種巖(yan)(yan)石極易風化發育成(cheng)(cheng)紫色(se)(se)土。紫色(se)(se)土含有豐富的(de)(de)(de)(de)鈣、磷、鉀等(deng)營養元素(su)，是(shi)南(nan)方(fang)(fang)最肥(fei)沃(wo)的(de)(de)(de)(de)自(zi)然土壤。四川(chuan)(chuan)盆(pen)(pen)地(di)(di)(di)(di)是(shi)全國紫色(se)(se)土分布最集(ji)中的(de)(de)(de)(de)地(di)(di)(di)(di)方(fang)(fang)，向有“紫色(se)(se)盆(pen)(pen)地(di)(di)(di)(di)”的(de)(de)(de)(de)美稱(cheng)。四川(chuan)(chuan)盆(pen)(pen)地(di)(di)(di)(di)底部面(mian)(mian)積約16萬多(duo)平(ping)方(fang)(fang)千米(mi)，按其地(di)(di)(di)(di)理差異，自(zi)西(xi)(xi)向東(dong)又可分為成(cheng)(cheng)都平(ping)原(yuan)(yuan)、川(chuan)(chuan)中丘(qiu)陵(ling)和(he)(he)川(chuan)(chuan)東(dong)平(ping)行嶺谷三部分。成(cheng)(cheng)都平(ping)原(yuan)(yuan)西(xi)(xi)方(fang)(fang)是(shi)龍(long)(long)門(men)山(shan)(shan)脈(mo)，東(dong)方(fang)(fang)是(shi)龍(long)(long)泉山(shan)(shan)脈(mo)。
四川盆地(di)(di)可明顯分為(wei)邊(bian)緣山(shan)地(di)(di)和盆地(di)(di)底部兩大部分，其面積(ji)分別(bie)約為(wei)10萬多和16多萬平(ping)方公(gong)里。邊(bian)緣山(shan)地(di)(di)多中山(shan)和低山(shan)。
景觀(guan)各要素過(guo)渡(du)性明顯，如(ru)動(dong)植(zhi)(zhi)物(wu)組(zu)(zu)成(cheng)上分(fen)別滲透了華(hua)中區(qu)(qu)(qu)、西南(nan)區(qu)(qu)(qu)、青藏高原區(qu)(qu)(qu)和華(hua)北(bei)區(qu)(qu)(qu)的(de)成(cheng)分(fen)。邊(bian)緣(yuan)山(shan)(shan)地(di)(di)區(qu)(qu)(qu)從下而上一(yi)般具有2～5個(ge)垂直自(zi)然分(fen)帶(dai)。邊(bian)緣(yuan)山(shan)(shan)地(di)(di)是四川多種經(jing)濟林木和用(yong)材林基地(di)(di)。農業上水土流失較為(wei)嚴重。盆地(di)(di)底(di)部多丘(qiu)陵、低(di)山(shan)(shan)和平原。地(di)(di)表組(zu)(zu)成(cheng)物(wu)質(zhi)新而單一(yi)，多砂泥巖與第四紀沉積物(wu)。氣候(hou)上屬中亞熱(re)帶(dai)，熱(re)量遠比邊(bian)緣(yuan)山(shan)(shan)地(di)(di)為(wei)高，但降(jiang)水量不及邊(bian)緣(yuan)山(shan)(shan)地(di)(di)。植(zhi)(zhi)被為(wei)人(ren)工(gong)的(de)次(ci)生林木所代替，覆(fu)被率低(di)，耕地(di)(di)連片，夏(xia)伏旱和洪澇是這一(yi)地(di)(di)區(qu)(qu)(qu)最大災害。
盆(pen)(pen)(pen)地(di)(di)內部(bu)地(di)(di)形地(di)(di)貌顯示(shi)出(chu)明(ming)顯的三(san)(san)分特(te)點，即盆(pen)(pen)(pen)西平原地(di)(di)貌、盆(pen)(pen)(pen)中丘陵地(di)(di)貌和盆(pen)(pen)(pen)東山(shan)地(di)(di)地(di)(di)貌，三(san)(san)者以龍泉(quan)山(shan)和華鎣山(shan)為界。
四(si)川(chuan)盆(pen)(pen)地其(qi)輪(lun)廓形態總體近似(si)長方形，形似(si)信封(feng)狀，右傾斜置在亞洲(zhou)大陸，因此被地理學者(zhe)稱之為信封(feng)盆(pen)(pen)地。信封(feng)盆(pen)(pen)地東部(bu)(bu)(bu)頂點云(yun)陽(yang)（靠(kao)(kao)近萬州），南(nan)部(bu)(bu)(bu)頂點敘永(靠(kao)(kao)近遵(zun)義)，西部(bu)(bu)(bu)頂點雅安，北部(bu)(bu)(bu)頂點廣(guang)元。信封(feng)盆(pen)(pen)地幾何中(zhong)心城(cheng)市(shi)遂寧（幾何中(zhong)心點大致在蓬溪南(nan)部(bu)(bu)(bu)地區），中(zhong)北部(bu)(bu)(bu)（內頂角）中(zhong)心城(cheng)市(shi)南(nan)充，中(zhong)南(nan)部(bu)(bu)(bu)內頂角安岳(yue)。
四川盆(pen)地西部的成都和(he)東南部的重慶皆為國家中心城市。
四川盆地(di)(di)由盆周山(shan)地(di)(di)和盆地(di)(di)底(di)部構成。
盆周東部(bu)為長江三(san)峽，南部(bu)為云貴高(gao)原，西部(bu)為青藏(zang)高(gao)原，北部(bu)為大巴山。
盆地底部主(zhu)要(yao)分(fen)(fen)為川(chuan)(chuan)(chuan)東平(ping)(ping)行嶺谷(gu)、川(chuan)(chuan)(chuan)中(zhong)丘陵(ling)和川(chuan)(chuan)(chuan)西成都(dou)平(ping)(ping)原三部分(fen)(fen)。龍泉山是成都(dou)平(ping)(ping)原和川(chuan)(chuan)(chuan)中(zhong)丘陵(ling)的界(jie)山，華鎣(ying)山是川(chuan)(chuan)(chuan)中(zhong)丘陵(ling)和川(chuan)(chuan)(chuan)東平(ping)(ping)行嶺谷(gu)的界(jie)山。
（1）在龍泉山和龍門山、邛崍山之間的(de)盆(pen)西(xi)平(ping)(ping)原，系(xi)斷裂下陷由(you)岷(min)(min)江(jiang)(jiang)水系(xi)的(de)河(he)流沖積而(er)成，面積約8000平(ping)(ping)方千(qian)米(mi)(mi)，為(wei)我國(guo)西(xi)南最大的(de)平(ping)(ping)原，因成都位于平(ping)(ping)原之中， 故稱(cheng)(cheng)成都平(ping)(ping)原。成都平(ping)(ping)原海拔460米(mi)(mi)～750米(mi)(mi)，地勢由(you)西(xi)北向(xiang)東(dong)南傾斜(xie)，地表平(ping)(ping)坦，相(xiang)對高(gao)差(cha)一般(ban)不超過30米(mi)(mi)～50米(mi)(mi)，它由(you)岷(min)(min)江(jiang)(jiang)、沱江(jiang)(jiang)、涪江(jiang)(jiang)、青衣江(jiang)(jiang)等八條河(he)流沖積聯綴而(er)成，土壤肥(fei)沃，河(he)渠稠密，有著(zhu)名的(de)都江(jiang)(jiang)堰自流灌溉(gai)，自古以(yi)來素有“天府”之稱(cheng)(cheng)。
（2）在(zai)龍泉山和華(hua)鎣山之間的盆中(zhong)丘陵，地勢低矮，海拔大多在(zai)300米(mi)～500米(mi)之間，相(xiang)對高(gao)差(cha)50米(mi)～150米(mi)，地勢由(you)北向(xiang)南傾(qing)斜，巖(yan)層近于水平，在(zai)流水的長期侵蝕切(qie)割作用下，形(xing)成臺階(jie)狀的方山丘陵，南部多淺丘，北部多深丘。丘陵地表軟(ruan)硬相(xiang)間的紫紅色砂、頁巖(yan)極易(yi)風化為(wei)紫色土，富含磷鉀(jia)，自然肥力較高(gao)，宜種性廣，是四(si)川全省糧食、經濟作物主產區。
（3）華鎣山(shan)(shan)以東為盆東平(ping)行嶺谷區，由多(duo)條(tiao)近東北西南走向的條(tiao)狀背斜(xie)山(shan)(shan)地(di)(di)(di)與向斜(xie)寬(kuan)谷組成，山(shan)(shan)地(di)(di)(di)陡而窄，高700米(mi)(mi)(mi)-1000米(mi)(mi)(mi)，其(qi)中，華鎣山(shan)(shan)高1705米(mi)(mi)(mi)，為盆地(di)(di)(di)底部最(zui)高峰(feng)。山(shan)(shan)地(di)(di)(di)頂部的石灰巖被雨水(shui)溶蝕后，常成凹槽，故山(shan)(shan)地(di)(di)(di)大多(duo)具(ju)有“一山(shan)(shan)二嶺一槽”或“一山(shan)(shan)三嶺二槽”的特(te)色(se)。山(shan)(shan)嶺間(jian)的谷地(di)(di)(di)寬(kuan)而緩，海拔300米(mi)(mi)(mi)～500米(mi)(mi)(mi)，其(qi)間(jian)丘陵(ling)、平(ping)壩交錯(cuo)分布，是平(ping)行嶺谷區工農(nong)業(ye)生產主要地(di)(di)(di)區。
四川(chuan)盆地邊緣(yuan)山(shan)地區屬(shu)強烈上(shang)升的褶皺帶。
地貌顯著特征是(shi)，海拔較高(gao)，過渡性明顯，均為(wei)(wei)一系列中山(shan)(shan)和低山(shan)(shan)所圍繞。盆地北緣米倉山(shan)(shan)、大(da)巴山(shan)(shan)近(jin)東西走向，是(shi)秦巴山(shan)(shan)地南翼部分，海拔一般在1500米～2200米之(zhi)間，山(shan)(shan)勢雄偉，山(shan)(shan)坡陡(dou)峭(qiao)，溝谷深切，相對(dui)高(gao)差(cha)(cha)可達500米～1000米；南緣大(da)婁山(shan)(shan)屬氣勢磅(bang)礴的(de)云(yun)貴高(gao)原之(zhi)一部分；西緣有龍門(men)山(shan)(shan)、邛(qiong)崍山(shan)(shan)、峨(e)(e)眉山(shan)(shan)，山(shan)(shan)脊海拔都在1500米至～3000米以上，相對(dui)高(gao)差(cha)(cha)可達1000米，屬中國地勢第一級階梯。峨(e)(e)眉山(shan)(shan)頂峰高(gao)3099米，與附近(jin)的(de)平原相對(dui)高(gao)差(cha)(cha)達2660米，山(shan)(shan)勢巍峨(e)(e)秀麗，為(wei)(wei)中國四(si)大(da)佛教名山(shan)(shan)之(zhi)一。
四(si)周為海拔2000～3000米的(de)山(shan)(shan)脈和高原所環繞，北面(mian)是(shi)大巴(ba)山(shan)(shan)、米倉(cang)山(shan)(shan)、龍門山(shan)(shan)，西面(mian)是(shi)青藏高原邊緣(yuan)的(de)邛崍(lai)山(shan)(shan)、大涼山(shan)(shan)，南面(mian)是(shi)大婁(lou)山(shan)(shan)，東面(mian)是(shi)巫山(shan)(shan)。
無論從構造(zao)還是(shi)人(ren)地(di)(di)(di)(di)(di)貌上看，四(si)(si)川盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)都(dou)是(shi)一(yi)個典型(xing)的(de)(de)(de)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)。它從震旦紀(ji)以來(lai)就是(shi)地(di)(di)(di)(di)(di)殼比較穩定的(de)(de)(de)大型(xing)拗陷區。晚三(san)迭紀(ji)的(de)(de)(de)印(yin)支運動中成(cheng)(cheng)(cheng)為(wei)(wei)(wei)一(yi)個內(nei)(nei)(nei)陸湖盆(pen)(pen)(pen)，但范圍(wei)要比今(jin)(jin)日的(de)(de)(de)四(si)(si)川大得多(duo)，中生(sheng)代(dai)堆積(ji)了厚達3000～4000米的(de)(de)(de)紫(zi)紅色的(de)(de)(de)砂巖(yan)和頁巖(yan)，因此人(ren)們又稱(cheng)它為(wei)(wei)(wei)“紅色盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)”或(huo)“紫(zi)色盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)”。中生(sheng)代(dai)末期的(de)(de)(de)四(si)(si)川運動使盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)周圍(wei)褶(zhe)(zhe)皺(zhou)成(cheng)(cheng)(cheng)山(shan)，中間(jian)相對(dui)下陷，輪(lun)廓基本形(xing)(xing)成(cheng)(cheng)(cheng)，盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)內(nei)(nei)(nei)部(bu)(bu)(bu)地(di)(di)(di)(di)(di)層也發生(sheng)大規模的(de)(de)(de)變形(xing)(xing)。東(dong)部(bu)(bu)(bu)出現一(yi)組(zu)北東(dong)向(xiang)的(de)(de)(de)褶(zhe)(zhe)皺(zhou)，稱(cheng)盆(pen)(pen)(pen)東(dong)褶(zhe)(zhe)皺(zhou)帶；中部(bu)(bu)(bu)形(xing)(xing)成(cheng)(cheng)(cheng)穹窿(long)構造(zao)，稱(cheng)盆(pen)(pen)(pen)中穹窿(long)帶；西部(bu)(bu)(bu)表現成(cheng)(cheng)(cheng)為(wei)(wei)(wei)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)沉(chen)陷帶，為(wei)(wei)(wei)今(jin)(jin)天盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)的(de)(de)(de)三(san)個地(di)(di)(di)(di)(di)貌區奠定了基礎。新生(sheng)代(dai)的(de)(de)(de)喜馬拉雅運動使周圍(wei)山(shan)地(di)(di)(di)(di)(di)再次上升，盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)再次相對(dui)下陷， 成(cheng)(cheng)(cheng)都(dou)一(yi)帶下陷更深。同(tong)時(shi)，長江切穿巫山(shan)，滾(gun)滾(gun)東(dong)流，完成(cheng)(cheng)(cheng)了統(tong)一(yi)的(de)(de)(de)長江水系，使內(nei)(nei)(nei)流盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)轉變為(wei)(wei)(wei)外(wai)流盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)。四(si)(si)川盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)可明顯分(fen)為(wei)(wei)(wei)邊緣(yuan)山(shan)地(di)(di)(di)(di)(di)和盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)底部(bu)(bu)(bu)兩大部(bu)(bu)(bu)分(fen)，其面(mian)積(ji)分(fen)別約為(wei)(wei)(wei)10萬(wan)(wan)多(duo)和16萬(wan)(wan)多(duo)平(ping)(ping)方千米。 四(si)(si)川盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)是(shi)我國(guo)最大的(de)(de)(de)外(wai)流盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)，面(mian)積(ji)26萬(wan)(wan)多(duo)平(ping)(ping)方千米。四(si)(si)川盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)內(nei)(nei)(nei)部(bu)(bu)(bu)丘(qiu)陵、平(ping)(ping)原交錯，地(di)(di)(di)(di)(di)勢北高南低。由(you)于地(di)(di)(di)(di)(di)表形(xing)(xing)態的(de)(de)(de)不同(tong)，以華鎣山(shan)、龍泉山(shan)為(wei)(wei)(wei)界。
盆底(di)可分(fen)為三部分(fen)：
①華鎣山以東(dong)為大致平(ping)行的川(chuan)東(dong)嶺谷，由(you)東(dong)北—西南走向的許多條狀(zhuang)山體組(zu)成，海拔一般(ban)在700～800米(mi)，谷地中多低丘(qiu)與平(ping)壩，海拔200～500米(mi)，是川(chuan)東(dong)農業和人口集中的地方(fang)。
②華鎣山(shan)和龍泉山(shan)之間(jian)為方(fang)山(shan)丘(qiu)陵，即川中丘(qiu)陵。區(qu)內(nei)由于紫(zi)紅色砂頁巖傾角平緩，受(shou)切割后形(xing)成大片(pian)方(fang)山(shan)式(shi)丘(qiu)陵。海拔(ba)350～450米(mi)，相(xiang)對高度幾(ji)十(shi)米(mi)。當地勞動人民利用方(fang)山(shan)山(shan)丘(qiu)土層深厚的(de)特點(dian)，把梯田(tian)一直修到山(shan)頂。
③龍泉山以西(xi)為(wei)平(ping)原。稱為(wei)川西(xi)平(ping)原或成都平(ping)原，面積6000多(duo)平(ping)方千(qian)米(mi)，是四川盆地最大的(de)(de)平(ping)原，也是西(xi)南地區(qu)最大的(de)(de)平(ping)原，海拔約600米(mi)。
四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)屬揚(yang)子準地(di)(di)(di)(di)(di)(di)臺四(si)川(chuan)臺坳。古(gu)生(sheng)代(dai)時(shi)相(xiang)對隆起(qi)，缺乏泥盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)系和(he)石(shi)(shi)炭系。印支(zhi)運動轉換為(wei)大(da)型拗陷，晚燕山(shan)(shan)(shan)(shan)(shan)運動，特(te)別是喜馬拉雅運動后(hou)發生(sheng)褶皺隆起(qi)。盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)的(de)(de)(de)(de)(de)(de)格局主(zhu)要(yao)受北(bei)東—南西(xi)向(xiang)及北(bei)西(xi)向(xiang)兩(liang)條構(gou)造線控(kong)制，構(gou)成(cheng)(cheng)了典型的(de)(de)(de)(de)(de)(de)菱(ling)(ling)形(xing)(xing)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)，四(si)川(chuan)廣元、四(si)川(chuan)雅安、四(si)川(chuan)敘永為(wei)菱(ling)(ling)形(xing)(xing)的(de)(de)(de)(de)(de)(de)四(si)頂點，東西(xi)兩(liang)邊(bian)稍長(chang)，為(wei)380～430公里，南北(bei)兩(liang)邊(bian)略短，為(wei)310～330公里。以上菱(ling)(ling)形(xing)(xing)四(si)頂點的(de)(de)(de)(de)(de)(de)連(lian)線與盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)內650～750米的(de)(de)(de)(de)(de)(de)等高線大(da)體相(xiang)當(dang)，盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)底(di)(di)部(bu)(bu)與邊(bian)緣山(shan)(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)也(ye)以此為(wei)分界。四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)在(zai)(zai)距今1.4億年以前，還(huan)是內陸湖(hu)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)。至(zhi)距今6.6千萬(wan)年時(shi)，盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)邊(bian)緣山(shan)(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)迅速隆升，長(chang)江中上游水(shui)系開(kai)始溝通(tong)。盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)內湖(hu)水(shui)東瀉奠定了現今之地(di)(di)(di)(di)(di)(di)貌形(xing)(xing)態(tai)。盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)邊(bian)緣多低(di)山(shan)(shan)(shan)(shan)(shan)和(he)中山(shan)(shan)(shan)(shan)(shan)，山(shan)(shan)(shan)(shan)(shan)勢(shi)陡峻，發源盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)邊(bian)緣山(shan)(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)的(de)(de)(de)(de)(de)(de)河(he)流大(da)多為(wei)“V”型谷(gu)，嶺谷(gu)高差都逾500～1 000米， 地(di)(di)(di)(di)(di)(di)表崎嶇，故歷史上就有(you)“蜀(shu)道難，難于(yu)上青天”之說。山(shan)(shan)(shan)(shan)(shan)脊海拔(ba)大(da)多在(zai)(zai)2000～3000米，西(xi)北(bei)部(bu)(bu)與西(xi)部(bu)(bu)可超(chao)過(guo)3000～4000米，如龍門(men)山(shan)(shan)(shan)(shan)(shan)4984米，峨眉山(shan)(shan)(shan)(shan)(shan)3099米，小相(xiang)嶺4 791米。地(di)(di)(di)(di)(di)(di)表廣泛(fan)出露古(gu)生(sheng)代(dai)及其以前的(de)(de)(de)(de)(de)(de)石(shi)(shi)灰(hui)(hui)巖(yan)(yan)(yan)，其次(ci)為(wei)板巖(yan)(yan)(yan)、片巖(yan)(yan)(yan)、結(jie)晶(jing)灰(hui)(hui)巖(yan)(yan)(yan)、石(shi)(shi)英(ying)巖(yan)(yan)(yan)、砂(sha)泥巖(yan)(yan)(yan)和(he)礫巖(yan)(yan)(yan)，局部(bu)(bu)有(you)花(hua)崗巖(yan)(yan)(yan)和(he)玄武巖(yan)(yan)(yan)。石(shi)(shi)灰(hui)(hui)巖(yan)(yan)(yan)分布區可見石(shi)(shi)林、溶洞、暗(an)河(he)、槽谷(gu)等喀(ka)斯特(te)地(di)(di)(di)(di)(di)(di)貌，盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)南緣興文縣素(su)有(you)“石(shi)(shi)林洞鄉(xiang)”之稱(cheng)(cheng)（見興文石(shi)(shi)林）。巫(wu)山(shan)(shan)(shan)(shan)(shan)十(shi)二峰和(he)金佛山(shan)(shan)(shan)(shan)(shan)等名(ming)山(shan)(shan)(shan)(shan)(shan)主(zhu)要(yao)也(ye)由(you)(you)石(shi)(shi)灰(hui)(hui)巖(yan)(yan)(yan)發育而成(cheng)(cheng)。由(you)(you)石(shi)(shi)灰(hui)(hui)巖(yan)(yan)(yan)、玄武巖(yan)(yan)(yan)、花(hua)崗巖(yan)(yan)(yan)等組成(cheng)(cheng)的(de)(de)(de)(de)(de)(de)峨眉山(shan)(shan)(shan)(shan)(shan)及由(you)(you)砂(sha)泥巖(yan)(yan)(yan)、礫巖(yan)(yan)(yan)組成(cheng)(cheng)的(de)(de)(de)(de)(de)(de)青城(cheng)山(shan)(shan)(shan)(shan)(shan)，素(su)有(you)“峨眉天下(xia)秀”、“青城(cheng)天下(xia)幽”之稱(cheng)(cheng)，為(wei)中國著名(ming)游覽勝地(di)(di)(di)(di)(di)(di)。盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)底(di)(di)部(bu)(bu)海拔(ba)多數在(zai)(zai)250～700米，地(di)(di)(di)(di)(di)(di)勢(shi)東南傾，盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)內各河(he)流均由(you)(you)邊(bian)緣山(shan)(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)匯聚盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)底(di)(di)部(bu)(bu)的(de)(de)(de)(de)(de)(de)長(chang)江干流，形(xing)(xing)成(cheng)(cheng)向(xiang)心(xin)狀水(shui)系。地(di)(di)(di)(di)(di)(di)表為(wei)大(da)面積的(de)(de)(de)(de)(de)(de)中生(sheng)代(dai)紫紅色砂(sha)巖(yan)(yan)(yan)與泥巖(yan)(yan)(yan)所覆蓋，故稱(cheng)(cheng)為(wei)“紅層(ceng)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)”，是中國中生(sheng)代(dai)陸相(xiang)紅層(ceng)分布最(zui)集中地(di)(di)(di)(di)(di)(di)區。四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)為(wei)丘(qiu)陵(ling)性(xing)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)，底(di)(di)部(bu)(bu)以丘(qiu)陵(ling)為(wei)主(zhu)，次(ci)為(wei)低(di)山(shan)(shan)(shan)(shan)(shan)和(he)平(ping)原。
四(si)川(chuan)盆地(di)(di)屬揚(yang)子陸(lu)(lu)臺一(yi)部(bu)分，稱為四(si)川(chuan)陸(lu)(lu)臺，屬較穩定的地(di)(di)區，但仍經(jing)過兩次(ci)大規模的海(hai)浸。第一(yi)次(ci)從5億多(duo)年前(qian)的寒武紀(ji)開始，延續(xu)到3.7億多(duo)年的志(zhi)留(liu)紀(ji)，不斷下陷(xian)(xian)成(cheng)了海(hai)洋盆地(di)(di)，志(zhi)留(liu)紀(ji)時(shi)發(fa)生加里東運動(dong)，除(chu)了西部(bu)的龍門山(shan)(shan)地(di)(di)槽(cao)繼續(xu)下陷(xian)(xian)外，其余地(di)(di)區上升(sheng)為陸(lu)(lu)。2.7億年前(qian)的石炭(tan)紀(ji)末(mo)，發(fa)生范(fan)圍更大的第二次(ci)海(hai)浸，盆地(di)(di)再次(ci)為海(hai)洋占據。二疊紀(ji)時(shi)海(hai)陸(lu)(lu)交替(ti)，形成(cheng)重慶附近的南酮、松(song)藻、天府(fu)等煤(mei)礦。二疊紀(ji)末(mo)，盆地(di)(di)西部(bu)巖漿噴(pen)出(chu)，峨(e)眉山(shan)(shan)小金(jin)頂(ding)及(ji)清音閣一(yi)帶的玄武巖就在(zai)這時(shi)生成(cheng)。
距今1.9億年(nian)的(de)(de)三(san)疊紀，“印支運動(dong)”使盆地(di)邊緣逐(zhu)漸隆起(qi)成山(shan)，被海水(shui)(shui)淹(yan)沒的(de)(de)地(di)區(qu)逐(zhu)漸上升成陸，由海盆轉為湖(hu)盆。當(dang)時(shi)湖(hu)水(shui)(shui)幾乎占據現今四(si)川盆地(di)的(de)(de)全境，稱為“蜀(shu)湖(hu)”，從(cong)此結束了海浸(jin)的(de)(de)歷史(shi)。在(zai)中(zhong)(zhong)生(sheng)代漫長的(de)(de)1億多年(nian)里，盆地(di)氣候溫暖(nuan)濕潤(run)，到(dao)(dao)處(chu)生(sheng)長蕨(jue)類、蘇鐵和(he)裸子(zi)植物，是(shi)(shi)(shi)又一(yi)(yi)個成煤期，永榮煤礦(kuang)即在(zai)三(san)疊紀和(he)侏羅紀時(shi)形(xing)成。東起(qi)長壽、墊江，西到(dao)(dao)江油、邛(qiong)崍，北抵大巴山(shan)麓(lu)，南到(dao)(dao)貴州赤水(shui)(shui)，還是(shi)(shi)(shi)天(tian)然氣富集區(qu)。這一(yi)(yi)時(shi)期爬行(xing)動(dong)物恐龍稱霸(ba)一(yi)(yi)時(shi)。1957年(nian)在(zai)合州發(fa)現的(de)(de)“合州馬門溪龍”身長22米，高3.5米，是(shi)(shi)(shi)中(zhong)(zhong)國亞洲最大和(he)最完整的(de)(de)恐龍化石。
7000萬(wan)(wan)年(nian)(nian)前的(de)(de)(de)(de)白堊紀(ji)末期，發(fa)生(sheng)又一(yi)次強(qiang)(qiang)烈(lie)的(de)(de)(de)(de)地(di)(di)(di)(di)(di)(di)殼運(yun)(yun)動“燕山(shan)運(yun)(yun)動”。盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)四(si)(si)周山(shan)地(di)(di)(di)(di)(di)(di)繼續隆起，同時(shi)產生(sheng)不少大(da)斷(duan)(duan)(duan)層(ceng)(ceng)(ceng)，如(ru)西(xi)部(bu)(bu)(bu)的(de)(de)(de)(de)龍門(men)山(shan)大(da)斷(duan)(duan)(duan)層(ceng)(ceng)(ceng)和(he)(he)東部(bu)(bu)(bu)的(de)(de)(de)(de)華瑩山(shan)大(da)斷(duan)(duan)(duan)層(ceng)(ceng)(ceng)，把盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)分為(wei)三部(bu)(bu)(bu)分。蜀湖(hu)縮小(xiao)為(wei)僅有2萬(wan)(wan)平方公里的(de)(de)(de)(de)蜀湖(hu)。封閉的(de)(de)(de)(de)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)地(di)(di)(di)(di)(di)(di)形(xing)(xing)及急劇(ju)縮小(xiao)的(de)(de)(de)(de)水面，使(shi)氣候逐漸(jian)變(bian)得干熱，沉(chen)積物(wu)由(you)海(hai)相(xiang)(xiang)、海(hai)陸交替相(xiang)(xiang)變(bian)為(wei)陸相(xiang)(xiang)，大(da)量(liang)風化、侵(qin)蝕、剝蝕的(de)(de)(de)(de)物(wu)質在盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)堆積了(le)(le)數千米(mi)厚，形(xing)(xing)成紅(hong)(hong)色和(he)(he)紫紅(hong)(hong)色的(de)(de)(de)(de)砂、泥(ni)、頁巖。裸子植(zhi)物(wu)不斷(duan)(duan)(duan)衰退，恐龍滅絕了(le)(le)。內陸湖(hu)泊(bo)在干燥條件(jian)下，經(jing)(jing)強(qiang)(qiang)烈(lie)蒸發(fa)，濃度增大(da)，鹽分不斷(duan)(duan)(duan)積累，形(xing)(xing)成鹽湖(hu)，后來(lai)泥(ni)沙掩埋而保存于地(di)(di)(di)(di)(di)(di)層(ceng)(ceng)(ceng)之中，經(jing)(jing)過漫長的(de)(de)(de)(de)地(di)(di)(di)(di)(di)(di)質作用形(xing)(xing)成巖層(ceng)(ceng)(ceng)，自貢一(yi)帶是著名(ming)的(de)(de)(de)(de)井鹽產地(di)(di)(di)(di)(di)(di)。 2000多萬(wan)(wan)年(nian)(nian)前的(de)(de)(de)(de)新第三紀(ji)，受喜馬拉雅造(zao)山(shan)運(yun)(yun)動的(de)(de)(de)(de)影響。距今二(er)、三百(bai)萬(wan)(wan)年(nian)(nian)的(de)(de)(de)(de)第四(si)(si)紀(ji)，地(di)(di)(di)(di)(di)(di)殼再次發(fa)生(sheng)構造(zao)運(yun)(yun)動。從(cong)而，四(si)(si)川(chuan)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)由(you)內流(liu)(liu)(liu)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)變(bian)為(wei)外流(liu)(liu)(liu)陸盆(pen)(pen)(pen)，由(you)封閉的(de)(de)(de)(de)內流(liu)(liu)(liu)區(qu)(qu)變(bian)為(wei)外流(liu)(liu)(liu)區(qu)(qu)，由(you)以(yi)堆積為(wei)主(zhu)變(bian)為(wei)侵(qin)蝕為(wei)主(zhu)，經(jing)(jing)歷了(le)(le)海(hai)盆(pen)(pen)(pen)——湖(hu)盆(pen)(pen)(pen)——陸盆(pen)(pen)(pen)的(de)(de)(de)(de)滄(cang)桑(sang)之變(bian)。 第四(si)(si)紀(ji)是冰川(chuan)廣布的(de)(de)(de)(de)時(shi)代(dai)，盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)西(xi)北山(shan)地(di)(di)(di)(di)(di)(di)發(fa)育大(da)量(liang)冰川(chuan)。冰川(chuan)消(xiao)融后，大(da)量(liang)沉(chen)積物(wu)由(you)岷江、沱江等攜帶，堆積在西(xi)部(bu)(bu)(bu)的(de)(de)(de)(de)凹(ao)陷區(qu)(qu)，即以(yi)前的(de)(de)(de)(de)蜀湖(hu)之中，最終形(xing)(xing)成了(le)(le)成都(dou)平原。 四(si)(si)川(chuan)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)地(di)(di)(di)(di)(di)(di)貌豐富，平原7%，丘陵(ling)52%，低山(shan)41%。
四(si)川(chuan)盆(pen)地(di)中植物近萬種(zhong)，古(gu)老而特(te)有(you)(you)(you)種(zhong)之(zhi)多為中國其他地(di)區所不及。在盆(pen)地(di)邊緣山(shan)地(di)及盆(pen)東平(ping)行嶺(ling)谷尚可(ke)見水杉(shan)(shan)、銀杉(shan)(shan)、鵝掌楸、檫木(mu)、三尖杉(shan)(shan)、珙桐、水青樹、連(lian)香(xiang)樹、領春(chun)木(mu)、金錢槭、蠟梅、杜仲、紅(hong)(hong)豆(dou)杉(shan)(shan)、鐘(zhong)萼木(mu)、福建(jian)柏、穗花(hua)杉(shan)(shan)、崖柏、木(mu)瓜紅(hong)(hong)等(deng)珍稀孑(jie)遺植物與(yu)(yu)特(te)有(you)(you)(you)種(zhong)。在濕熱河谷可(ke)見桫欏、小羽桫欏、烏毛蕨、華南紫萁、里白(bai)等(deng)古(gu)熱帶孑(jie)遺植物。 四(si)川(chuan)盆(pen)地(di)的(de)地(di)帶性植被是(shi)亞(ya)熱帶常(chang)綠闊(kuo)(kuo)葉(xie)林(lin)，其代表樹種(zhong)有(you)(you)(you)栲(kao)樹、峨眉栲(kao)、刺果(guo)米櫧、青岡(gang)、曼(man)青岡(gang)、包石櫟、華木(mu)荷、大(da)包木(mu)荷、四(si)川(chuan)大(da)頭茶(cha)、楨楠、潤楠等(deng)，海拔一般情況下(xia)在1600～1 800米以下(xia)。其次(ci)有(you)(you)(you)馬尾(wei)松、杉(shan)(shan)木(mu)、柏木(mu)組成 的(de)亞(ya)熱帶針葉(xie)林(lin)及竹林(lin)。 邊緣山(shan)地(di)從(cong)下(xia)而上是(shi)常(chang)綠闊(kuo)(kuo)葉(xie)林(lin)、常(chang)綠闊(kuo)(kuo)葉(xie)與(yu)(yu)落葉(xie)闊(kuo)(kuo)葉(xie)混(hun)交林(lin)，寒溫(wen)帶山(shan)地(di)針葉(xie)林(lin)，局部有(you)(you)(you)亞(ya)高山(shan)灌(guan)叢草甸。
四川(chuan)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)是(shi)中(zhong)(zhong)國動(dong)(dong)(dong)物(wu)(wu)(wu)種(zhong)(zhong)類最(zui)多、最(zui)齊全(quan)(quan)的(de)(de)(de)地(di)(di)(di)(di)(di)區(qu)之一。據(ju)統計，除(chu)魚類外，盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)底部共有動(dong)(dong)(dong)物(wu)(wu)(wu)417種(zhong)(zhong)，盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)西(xi)緣(yuan)、北(bei)緣(yuan)和(he)南緣(yuan)山(shan)地(di)(di)(di)(di)(di)分別為(wei)487種(zhong)(zhong)、317種(zhong)(zhong)與288種(zhong)(zhong)，其(qi)中(zhong)(zhong)經(jing)濟(ji)動(dong)(dong)(dong)物(wu)(wu)(wu)均占一半以上(shang)。盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)西(xi)緣(yuan)山(shan)地(di)(di)(di)(di)(di)是(shi)中(zhong)(zhong)國特有而古老動(dong)(dong)(dong)物(wu)(wu)(wu)保(bao)(bao)(bao)存最(zui)好、最(zui)集中(zhong)(zhong)的(de)(de)(de)地(di)(di)(di)(di)(di)區(qu)，屬于(yu)一類保(bao)(bao)(bao)護(hu)動(dong)(dong)(dong)物(wu)(wu)(wu)的(de)(de)(de)有大(da)熊貓(mao)、金(jin)絲猴(hou)、扭角(jiao)羚、灰金(jin)絲猴(hou)、白(bai)唇鹿等(deng)。還有珍貴特有動(dong)(dong)(dong)物(wu)(wu)(wu)小(xiao)熊貓(mao)、雪豹、鬣(lie)羚、短尾猴(hou)、獼猴(hou)、毛冠鹿、水(shui)獺(ta)及鴛鴦、血(xue)雉(zhi)(zhi)、紅腹(fu)角(jiao)雉(zhi)(zhi)、綠尾虹雉(zhi)(zhi)、白(bai)腹(fu)錦雞、紅腹(fu)錦雞等(deng)。 盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)西(xi)緣(yuan)的(de)(de)(de)平武、青川(chuan)、北(bei)川(chuan)、寶興、天全(quan)(quan)、洪(hong)雅、馬(ma)邊等(deng)地(di)(di)(di)(di)(di)，均為(wei)中(zhong)(zhong)國大(da)熊貓(mao)的(de)(de)(de)主(zhu)要分布區(qu)。已設(she)立(li)唐(tang)家河(he)、王朗、臥龍（見(jian)臥龍自然保(bao)(bao)(bao)護(hu)區(qu)）、蜂桶寨、喇(la)叭河(he)等(deng)7處(chu)大(da)熊貓(mao)、金(jin)絲猴(hou)等(deng)自然保(bao)(bao)(bao)護(hu)區(qu)。 酉陽、馬(ma)邊、平武等(deng)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)邊緣(yuan)山(shan)地(di)(di)(di)(di)(di)溪溝中(zhong)(zhong)的(de)(de)(de)大(da)鯢(ni)及長江、金(jin)沙江中(zhong)(zhong)的(de)(de)(de)中(zhong)(zhong)華鱘(xun)、白(bai)鱘(xun)也(ye)為(wei)四川(chuan)所特有，均屬國家保(bao)(bao)(bao)護(hu)動(dong)(dong)(dong)物(wu)(wu)(wu)。
四(si)川(chuan)(chuan)盆地(di)有(you)煤、鐵(tie)、天然(ran)氣(qi)、石(shi)(shi)油(you)、鹽、芒硝(xiao)、石(shi)(shi)膏、磷、硫(liu)、鋁、金(jin)、銅、錳、石(shi)(shi)墨、汞等礦(kuang)產(chan)資源，其中(zhong)(zhong)(zhong)天然(ran)氣(qi)、芒硝(xiao)為全中(zhong)(zhong)(zhong)國之冠，并有(you)中(zhong)(zhong)(zhong)國重要的鍶(si)礦(kuang)。川(chuan)(chuan)東北(bei)是世(shi)界最大(da)的天然(ran)氣(qi)富(fu)集區(qu)之一，川(chuan)(chuan)中(zhong)(zhong)(zhong)和(he)南充等地(di)鹽巖(yan)礦(kuang)儲(chu)量很大(da)。
四川盆(pen)地(di)地(di)形閉塞，由于(yu)(yu)北(bei)部秦嶺阻擋冷(leng)空氣，冬(dong)季氣溫高于(yu)(yu)同(tong)緯(wei)度(du)(du)其(qi)他地(di)區。最(zui)冷(leng)月(yue)(yue)北(bei)部均(jun)溫3～5℃，南部5~8℃，較(jiao)同(tong)緯(wei)度(du)(du)的上(shang)海(hai)、湖(hu)北(bei)、安徽及緯(wei)度(du)(du)偏南的貴(gui)州高1～4℃。盆(pen)地(di)北(bei)部極(ji)端最(zui)低(di)溫-8～-5℃，南部-5℃~-2℃。霜(shuang)(shuang)雪少見，年(nian)無霜(shuang)(shuang)期長(chang)(chang)(chang)280～350天，同(tong)緯(wei)度(du)(du)上(shang)的武漢(han)冬(dong)天卻(que)霜(shuang)(shuang)雪不斷，盆(pen)地(di)位于(yu)(yu)長(chang)(chang)(chang)江河(he)谷中的長(chang)(chang)(chang)寧全年(nian)無霜(shuang)(shuang)。 盆(pen)地(di)各地(di)夏季始于(yu)(yu)5月(yue)(yue)底，終于(yu)(yu)9月(yue)(yue)中旬，夏長(chang)(chang)(chang)4個(ge)月(yue)(yue)，溫度(du)(du)上(shang)東高西低(di)。盆(pen)地(di)西部夏天平均(jun)氣溫約25℃，較(jiao)同(tong)緯(wei)度(du)(du)的上(shang)海(hai)、武漢(han)等城市偏低(di)3-4度(du)(du)，但濕(shi)度(du)(du)較(jiao)大(da)，所以(yi)悶熱難忍(ren)。
東(dong)部(bu)最熱(re)月氣(qi)溫(wen)(wen)高(gao)(gao)達26～29℃，長江(jiang)河谷局地(di)達到30℃。盛夏(xia)連晴(qing)高(gao)(gao)溫(wen)(wen)天氣(qi)又造成盆(pen)地(di)東(dong)南部(bu)嚴(yan)重的夏(xia)伏旱。盆(pen)地(di)氣(qi)溫(wen)(wen)東(dong)南高(gao)(gao)西(xi)(xi)北低(di)(di)，盆(pen)底高(gao)(gao)邊緣低(di)(di)； 各(ge)地(di)年(nian)均(jun)溫(wen)(wen)16～18℃。10℃以(yi)上(shang)活動積溫(wen)(wen)4500～6000℃，持續期8～9個(ge)月，屬中(zhong)亞(ya)熱(re)帶。東(dong)南部(bu)的長江(jiang)河谷積溫(wen)(wen)超過6000℃，相(xiang)當(dang)于中(zhong)國南嶺以(yi)南的南亞(ya)熱(re)帶氣(qi)候(hou)。盆(pen)地(di)氣(qi)溫(wen)(wen)東(dong)高(gao)(gao)西(xi)(xi)低(di)(di)，南高(gao)(gao)北低(di)(di)，盆(pen)底高(gao)(gao)而邊緣低(di)(di)，等溫(wen)(wen)線(xian)分布(bu)呈現同心圓狀。盆(pen)地(di)邊緣山地(di)氣(qi)溫(wen)(wen)具(ju)有垂直(zhi)分布(bu)特點，如(ru)峨眉山、金佛山海(hai)拔升高(gao)(gao)百米(mi)，氣(qi)溫(wen)(wen)遞減0.55℃和0.61℃。峨眉山頂年(nian)均(jun)溫(wen)(wen)僅(jin)3℃，10℃以(yi)上(shang)活動積溫(wen)(wen)586℃，氣(qi)候(hou)上(shang)相(xiang)當(dang)于寒(han)溫(wen)(wen)帶和亞(ya)寒(han)帶。
四川盆地(di)年(nian)降(jiang)水(shui)量(liang)1000～1300毫米，盆地(di)邊(bian)緣(yuan)(yuan)山(shan)地(di)降(jiang)水(shui)十分充沛，如樂山(shan)和雅(ya)安(an)間的(de)西緣(yuan)(yuan)山(shan)地(di)年(nian)降(jiang)水(shui)量(liang)為(wei)(wei)1 500～1800毫米，為(wei)(wei)中(zhong)國(guo)突出(chu)的(de)多(duo)雨區(qu)，有“華西雨屏(ping)”之(zhi)稱。但冬干、春旱、夏(xia)澇、秋綿雨，年(nian)內分配不(bu)均(jun)，70～75%的(de)雨量(liang)集中(zhong)于6～10月。最大(da)日降(jiang)水(shui)量(liang)可達300～500毫米。“巴山(shan)夜雨”自古聞名，夜雨占總雨量(liang)的(de)60～70%以上(shang)。盆地(di)區(qu)霧大(da)濕(shi)重，云(yun)低陰(yin)天(tian)多(duo)。峨眉山(shan)、金(jin)佛山(shan)是(shi)中(zhong)國(guo)霧日最多(duo)地(di)區(qu)之(zhi)一，年(nian)相(xiang)對濕(shi)度之(zhi)高也為(wei)(wei)中(zhong)國(guo)之(zhi)冠(guan)。盆地(di)年(nian)日照(zhao)僅900～1300小時，年(nian)太陽輻射(she)量(liang)為(wei)(wei)370～420千焦耳(er)/平方厘米，均(jun)為(wei)(wei)中(zhong)國(guo)最低值，故有“蜀犬(quan)吠(fei)日”之(zhi)說。
