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四(si)川盆(pen)地聚居著四(si)川省和重(zhong)慶市大部(bu)分人口、居民主(zhu)要(yao)為漢族巴(ba)蜀民系。是中國和世界上人口最多(duo)的區域之一。
中國(guo)著名紅層盆地，中國(guo)各大盆地中形態(tai)最典型(xing)、緯度最南、海拔最低(di)的盆地。位(wei)于(yu)長(chang)(chang)江上游(you)地區(qu)，海拔500米(mi)左右，長(chang)(chang)江把它(ta)和(he)東海一脈相連，它(ta)是中國(guo)最大的外流盆地。
四川(chuan)盆(pen)(pen)(pen)地(di)(di)(di)的(de)(de)(de)面(mian)積(ji)約26萬余平方千米（面(mian)積(ji)是(shi)居第五第六位的(de)(de)(de)兩湖盆(pen)(pen)(pen)地(di)(di)(di)和(he)銀額盆(pen)(pen)(pen)地(di)(di)(di)的(de)(de)(de)兩倍），占四川(chuan)省面(mian)積(ji)的(de)(de)(de)46%。四川(chuan)盆(pen)(pen)(pen)地(di)(di)(di)西依青藏高原(yuan)(yuan)和(he)橫斷山(shan)(shan)脈(mo)(mo)，北(bei)(bei)(bei)近(jin)秦巴(ba)山(shan)(shan)脈(mo)(mo)，與(yu)漢中(zhong)(zhong)盆(pen)(pen)(pen)地(di)(di)(di)相望，東(dong)接湘鄂西山(shan)(shan)地(di)(di)(di)，南(nan)連(lian)云貴(gui)高原(yuan)(yuan)，盆(pen)(pen)(pen)地(di)(di)(di)北(bei)(bei)(bei)緣米倉山(shan)(shan)，南(nan)緣大(da)婁山(shan)(shan)，東(dong)緣巫(wu)山(shan)(shan)，西緣邛崍(lai)山(shan)(shan)，西北(bei)(bei)(bei)邊(bian)(bian)緣龍門山(shan)(shan)，東(dong)北(bei)(bei)(bei)邊(bian)(bian)緣大(da)巴(ba)山(shan)(shan)，西南(nan)邊(bian)(bian)緣大(da)涼山(shan)(shan)，東(dong)南(nan)邊(bian)(bian)緣相望于(yu)武陵山(shan)(shan)。這里的(de)(de)(de)巖石，主要由紫(zi)紅(hong)色砂(sha)巖和(he)頁巖組成(cheng)。這兩種巖石極易風化(hua)發育成(cheng)紫(zi)色土(tu)。紫(zi)色土(tu)含有豐富的(de)(de)(de)鈣、磷、鉀等(deng)營(ying)養(yang)元素，是(shi)南(nan)方最肥(fei)沃的(de)(de)(de)自然土(tu)壤。四川(chuan)盆(pen)(pen)(pen)地(di)(di)(di)是(shi)全國紫(zi)色土(tu)分(fen)布最集中(zhong)(zhong)的(de)(de)(de)地(di)(di)(di)方，向(xiang)有“紫(zi)色盆(pen)(pen)(pen)地(di)(di)(di)”的(de)(de)(de)美稱。四川(chuan)盆(pen)(pen)(pen)地(di)(di)(di)底部(bu)面(mian)積(ji)約16萬多(duo)平方千米，按其地(di)(di)(di)理差異，自西向(xiang)東(dong)又可分(fen)為成(cheng)都平原(yuan)(yuan)、川(chuan)中(zhong)(zhong)丘陵和(he)川(chuan)東(dong)平行嶺谷(gu)三部(bu)分(fen)。成(cheng)都平原(yuan)(yuan)西方是(shi)龍門山(shan)(shan)脈(mo)(mo)，東(dong)方是(shi)龍泉山(shan)(shan)脈(mo)(mo)。
四川(chuan)盆地可(ke)明顯分(fen)(fen)為邊緣(yuan)(yuan)山地和盆地底部(bu)兩大(da)部(bu)分(fen)(fen)，其面積(ji)分(fen)(fen)別約為10萬多(duo)和16多(duo)萬平方公里。邊緣(yuan)(yuan)山地多(duo)中山和低山。
景觀(guan)各要素過渡性明顯(xian)，如動(dong)植物(wu)組(zu)成(cheng)上分別滲透了華中(zhong)區(qu)、西南區(qu)、青藏高(gao)原區(qu)和華北區(qu)的成(cheng)分。邊(bian)緣山(shan)(shan)地區(qu)從下而上一(yi)般具有2～5個垂直自然分帶。邊(bian)緣山(shan)(shan)地是(shi)(shi)四川多(duo)種(zhong)經濟林木和用(yong)材林基地。農業上水土流(liu)失(shi)較為嚴重(zhong)。盆(pen)地底部多(duo)丘陵、低(di)(di)山(shan)(shan)和平原。地表組(zu)成(cheng)物(wu)質新而單一(yi)，多(duo)砂泥巖與第四紀(ji)沉積物(wu)。氣候(hou)上屬(shu)中(zhong)亞熱帶，熱量遠比邊(bian)緣山(shan)(shan)地為高(gao)，但降水量不及邊(bian)緣山(shan)(shan)地。植被為人工的次生(sheng)林木所(suo)代(dai)替，覆被率低(di)(di)，耕地連片(pian)，夏伏(fu)旱(han)和洪(hong)澇是(shi)(shi)這一(yi)地區(qu)最大(da)災害(hai)。
盆(pen)地(di)內部(bu)地(di)形地(di)貌顯(xian)示出明顯(xian)的三(san)分特點，即盆(pen)西平原地(di)貌、盆(pen)中丘陵(ling)地(di)貌和盆(pen)東山(shan)(shan)地(di)地(di)貌，三(san)者以龍泉山(shan)(shan)和華鎣山(shan)(shan)為界。
四川盆地(di)其輪廓形態(tai)總(zong)體(ti)近似(si)長方形，形似(si)信(xin)封狀，右傾(qing)斜(xie)置(zhi)在亞洲大(da)陸，因此被地(di)理(li)學者稱之為(wei)信(xin)封盆地(di)。信(xin)封盆地(di)東部(bu)頂(ding)點(dian)云陽(yang)（靠(kao)近萬州），南部(bu)頂(ding)點(dian)敘永(靠(kao)近遵義(yi))，西部(bu)頂(ding)點(dian)雅安，北部(bu)頂(ding)點(dian)廣元。信(xin)封盆地(di)幾何中(zhong)心(xin)城市遂(sui)寧（幾何中(zhong)心(xin)點(dian)大(da)致在蓬溪(xi)南部(bu)地(di)區），中(zhong)北部(bu)（內頂(ding)角(jiao)）中(zhong)心(xin)城市南充，中(zhong)南部(bu)內頂(ding)角(jiao)安岳(yue)。
四(si)川盆(pen)地西部(bu)的成都和東南(nan)部(bu)的重慶皆為國家(jia)中心城市。
四川(chuan)盆地由盆周山地和盆地底部構成。
盆(pen)周東部(bu)為(wei)長江三峽，南部(bu)為(wei)云貴高原，西(xi)部(bu)為(wei)青藏高原，北部(bu)為(wei)大巴山。
盆地底部主要分為(wei)川(chuan)(chuan)東平行嶺谷、川(chuan)(chuan)中(zhong)丘陵和(he)川(chuan)(chuan)西成都平原三部分。龍泉山(shan)是成都平原和(he)川(chuan)(chuan)中(zhong)丘陵的界(jie)山(shan)，華鎣山(shan)是川(chuan)(chuan)中(zhong)丘陵和(he)川(chuan)(chuan)東平行嶺谷的界(jie)山(shan)。
（1）在龍泉山(shan)(shan)和龍門山(shan)(shan)、邛崍山(shan)(shan)之間的(de)盆西(xi)平(ping)原(yuan)，系(xi)斷裂(lie)下陷由(you)岷(min)江(jiang)(jiang)水系(xi)的(de)河(he)流沖(chong)積(ji)而成，面(mian)積(ji)約8000平(ping)方千米，為(wei)我國西(xi)南(nan)最(zui)大的(de)平(ping)原(yuan)，因成都(dou)位于平(ping)原(yuan)之中， 故(gu)稱成都(dou)平(ping)原(yuan)。成都(dou)平(ping)原(yuan)海拔460米～750米，地(di)勢由(you)西(xi)北向東南(nan)傾斜，地(di)表平(ping)坦，相對高(gao)差一般不超過30米～50米，它由(you)岷(min)江(jiang)(jiang)、沱江(jiang)(jiang)、涪江(jiang)(jiang)、青衣(yi)江(jiang)(jiang)等八條河(he)流沖(chong)積(ji)聯綴而成，土壤(rang)肥沃，河(he)渠稠密，有著名的(de)都(dou)江(jiang)(jiang)堰自流灌溉，自古以來素有“天府”之稱。
（2）在龍泉山(shan)(shan)(shan)和華(hua)鎣山(shan)(shan)(shan)之(zhi)間的(de)盆中(zhong)丘(qiu)(qiu)陵，地(di)勢低矮，海拔(ba)大多(duo)(duo)在300米～500米之(zhi)間，相(xiang)對高差50米～150米，地(di)勢由(you)北(bei)向(xiang)南(nan)傾斜，巖(yan)層近于水平，在流(liu)水的(de)長(chang)期侵蝕(shi)切割(ge)作用(yong)下，形成(cheng)臺(tai)階(jie)狀(zhuang)的(de)方(fang)山(shan)(shan)(shan)丘(qiu)(qiu)陵，南(nan)部多(duo)(duo)淺丘(qiu)(qiu)，北(bei)部多(duo)(duo)深丘(qiu)(qiu)。丘(qiu)(qiu)陵地(di)表軟(ruan)硬相(xiang)間的(de)紫紅色砂(sha)、頁巖(yan)極易(yi)風化為(wei)紫色土，富含磷(lin)鉀，自然肥力較(jiao)高，宜種性(xing)廣，是四(si)川全省糧(liang)食(shi)、經濟作物主產區。
（3）華鎣山以東(dong)為盆東(dong)平(ping)行(xing)嶺(ling)谷區，由多條近東(dong)北西南走向的條狀背斜山地(di)(di)與向斜寬(kuan)谷組成，山地(di)(di)陡而窄(zhai)，高(gao)700米(mi)(mi)-1000米(mi)(mi)，其(qi)中，華鎣山高(gao)1705米(mi)(mi)，為盆地(di)(di)底部最高(gao)峰。山地(di)(di)頂部的石(shi)灰巖被雨水溶蝕后，常成凹槽，故山地(di)(di)大多具(ju)有“一(yi)山二(er)嶺(ling)一(yi)槽”或“一(yi)山三嶺(ling)二(er)槽”的特色。山嶺(ling)間的谷地(di)(di)寬(kuan)而緩(huan)，海拔(ba)300米(mi)(mi)～500米(mi)(mi)，其(qi)間丘陵、平(ping)壩交錯分布，是平(ping)行(xing)嶺(ling)谷區工(gong)農業生產主(zhu)要地(di)(di)區。
四川盆(pen)地邊(bian)緣山地區屬(shu)強(qiang)烈上升的褶皺帶。
地(di)貌顯(xian)著特征是，海(hai)(hai)拔(ba)較(jiao)高(gao)，過渡性明顯(xian)，均為(wei)一(yi)系列中(zhong)(zhong)山和低山所(suo)圍繞。盆地(di)北緣(yuan)米(mi)(mi)倉山、大(da)巴(ba)山近(jin)東(dong)西走向，是秦巴(ba)山地(di)南翼部分，海(hai)(hai)拔(ba)一(yi)般在1500米(mi)(mi)～2200米(mi)(mi)之間，山勢雄偉，山坡陡峭，溝谷深切，相對高(gao)差(cha)可達500米(mi)(mi)～1000米(mi)(mi)；南緣(yuan)大(da)婁(lou)山屬氣勢磅礴的云貴高(gao)原之一(yi)部分；西緣(yuan)有龍門山、邛崍山、峨(e)(e)眉山，山脊海(hai)(hai)拔(ba)都在1500米(mi)(mi)至～3000米(mi)(mi)以上，相對高(gao)差(cha)可達1000米(mi)(mi)，屬中(zhong)(zhong)國(guo)地(di)勢第(di)一(yi)級階梯。峨(e)(e)眉山頂峰高(gao)3099米(mi)(mi)，與附近(jin)的平原相對高(gao)差(cha)達2660米(mi)(mi)，山勢巍(wei)峨(e)(e)秀麗，為(wei)中(zhong)(zhong)國(guo)四(si)大(da)佛教名山之一(yi)。
四周為海拔2000～3000米的(de)山(shan)脈和高原所環繞(rao)，北面是大(da)巴山(shan)、米倉山(shan)、龍(long)門山(shan)，西面是青(qing)藏高原邊緣的(de)邛崍山(shan)、大(da)涼山(shan)，南面是大(da)婁山(shan)，東面是巫山(shan)。
無論從(cong)構造還是(shi)人地(di)(di)(di)(di)(di)(di)貌上看，四川(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)都是(shi)一(yi)個典型的(de)(de)(de)(de)(de)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)。它(ta)從(cong)震(zhen)旦紀(ji)以(yi)來(lai)就是(shi)地(di)(di)(di)(di)(di)(di)殼(ke)比較穩定的(de)(de)(de)(de)(de)大(da)型拗陷(xian)區。晚(wan)三迭紀(ji)的(de)(de)(de)(de)(de)印支運(yun)動中(zhong)(zhong)(zhong)成(cheng)(cheng)為(wei)(wei)一(yi)個內(nei)陸(lu)湖盆(pen)(pen)(pen)(pen)，但(dan)范圍(wei)要比今(jin)日的(de)(de)(de)(de)(de)四川(chuan)大(da)得(de)多，中(zhong)(zhong)(zhong)生(sheng)(sheng)代(dai)堆積了厚達3000～4000米的(de)(de)(de)(de)(de)紫紅色(se)的(de)(de)(de)(de)(de)砂(sha)巖和頁巖，因此人們又稱它(ta)為(wei)(wei)“紅色(se)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)”或(huo)“紫色(se)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)”。中(zhong)(zhong)(zhong)生(sheng)(sheng)代(dai)末期的(de)(de)(de)(de)(de)四川(chuan)運(yun)動使盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)周圍(wei)褶(zhe)(zhe)皺成(cheng)(cheng)山(shan)，中(zhong)(zhong)(zhong)間相對(dui)下(xia)(xia)陷(xian)，輪廓基本形成(cheng)(cheng)，盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)內(nei)部(bu)(bu)(bu)地(di)(di)(di)(di)(di)(di)層也發(fa)生(sheng)(sheng)大(da)規模(mo)的(de)(de)(de)(de)(de)變形。東(dong)部(bu)(bu)(bu)出現(xian)一(yi)組北東(dong)向的(de)(de)(de)(de)(de)褶(zhe)(zhe)皺，稱盆(pen)(pen)(pen)(pen)東(dong)褶(zhe)(zhe)皺帶(dai)；中(zhong)(zhong)(zhong)部(bu)(bu)(bu)形成(cheng)(cheng)穹窿構造，稱盆(pen)(pen)(pen)(pen)中(zhong)(zhong)(zhong)穹窿帶(dai)；西部(bu)(bu)(bu)表現(xian)成(cheng)(cheng)為(wei)(wei)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)沉陷(xian)帶(dai)，為(wei)(wei)今(jin)天盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)的(de)(de)(de)(de)(de)三個地(di)(di)(di)(di)(di)(di)貌區奠(dian)定了基礎。新生(sheng)(sheng)代(dai)的(de)(de)(de)(de)(de)喜馬(ma)拉雅運(yun)動使周圍(wei)山(shan)地(di)(di)(di)(di)(di)(di)再次(ci)上升，盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)再次(ci)相對(dui)下(xia)(xia)陷(xian)， 成(cheng)(cheng)都一(yi)帶(dai)下(xia)(xia)陷(xian)更深(shen)。同時，長江切穿巫(wu)山(shan)，滾滾東(dong)流，完成(cheng)(cheng)了統一(yi)的(de)(de)(de)(de)(de)長江水(shui)系，使內(nei)流盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)轉變為(wei)(wei)外流盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)。四川(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)可明顯分(fen)為(wei)(wei)邊(bian)緣山(shan)地(di)(di)(di)(di)(di)(di)和盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)底部(bu)(bu)(bu)兩大(da)部(bu)(bu)(bu)分(fen)，其面(mian)積分(fen)別(bie)約(yue)為(wei)(wei)10萬多和16萬多平方千米。 四川(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)是(shi)我國最大(da)的(de)(de)(de)(de)(de)外流盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)，面(mian)積26萬多平方千米。四川(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)內(nei)部(bu)(bu)(bu)丘(qiu)陵、平原交錯，地(di)(di)(di)(di)(di)(di)勢北高(gao)南低。由于(yu)地(di)(di)(di)(di)(di)(di)表形態的(de)(de)(de)(de)(de)不同，以(yi)華鎣(ying)山(shan)、龍泉山(shan)為(wei)(wei)界。
盆底可分為三部(bu)分：
①華鎣山以東為大致平行的川(chuan)東嶺谷，由東北(bei)—西南走向的許多(duo)條狀山體組成，海拔一般在(zai)700～800米，谷地中(zhong)多(duo)低丘與平壩(ba)，海拔200～500米，是川(chuan)東農業和人口集中(zhong)的地方(fang)。
②華鎣山(shan)和龍泉山(shan)之間(jian)為(wei)方(fang)山(shan)丘陵(ling)，即川中丘陵(ling)。區內由于紫(zi)紅色砂頁巖傾角平緩，受(shou)切割后形(xing)成大(da)片方(fang)山(shan)式丘陵(ling)。海拔(ba)350～450米，相對高度幾十米。當(dang)地(di)勞(lao)動人(ren)民利用方(fang)山(shan)山(shan)丘土層(ceng)深厚的(de)特點，把梯(ti)田一直修到山(shan)頂。
③龍(long)泉(quan)山以西為平(ping)原。稱(cheng)為川(chuan)西平(ping)原或成都平(ping)原，面(mian)積6000多(duo)平(ping)方千米(mi)，是四川(chuan)盆地最大(da)的平(ping)原，也(ye)是西南(nan)地區最大(da)的平(ping)原，海拔(ba)約(yue)600米(mi)。
四川(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)屬揚子準(zhun)地(di)(di)(di)(di)(di)(di)(di)(di)(di)臺四川(chuan)臺坳(ao)。古生代(dai)時相對隆起，缺乏(fa)泥(ni)(ni)盆(pen)(pen)(pen)(pen)系和(he)(he)石(shi)炭系。印支(zhi)運(yun)(yun)動(dong)轉換為(wei)(wei)(wei)(wei)大(da)型拗陷，晚燕(yan)山(shan)(shan)(shan)(shan)(shan)(shan)運(yun)(yun)動(dong)，特(te)別(bie)是喜馬拉雅運(yun)(yun)動(dong)后發(fa)生褶(zhe)皺隆起。盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)的(de)(de)格局(ju)主(zhu)要(yao)受北(bei)東—南西(xi)(xi)向(xiang)及(ji)(ji)北(bei)西(xi)(xi)向(xiang)兩(liang)條構(gou)造線控制，構(gou)成了(le)典型的(de)(de)菱(ling)形盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)，四川(chuan)廣元、四川(chuan)雅安、四川(chuan)敘永為(wei)(wei)(wei)(wei)菱(ling)形的(de)(de)四頂點，東西(xi)(xi)兩(liang)邊(bian)(bian)稍長(chang)(chang)(chang)，為(wei)(wei)(wei)(wei)380～430公里，南北(bei)兩(liang)邊(bian)(bian)略短，為(wei)(wei)(wei)(wei)310～330公里。以(yi)(yi)上(shang)菱(ling)形四頂點的(de)(de)連線與盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)內(nei)650～750米(mi)(mi)的(de)(de)等(deng)(deng)高(gao)線大(da)體(ti)相當，盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)底部(bu)與邊(bian)(bian)緣(yuan)(yuan)山(shan)(shan)(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)(di)(di)(di)也以(yi)(yi)此(ci)為(wei)(wei)(wei)(wei)分界。四川(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)在(zai)距(ju)今1.4億年(nian)以(yi)(yi)前，還(huan)是內(nei)陸湖盆(pen)(pen)(pen)(pen)。至距(ju)今6.6千(qian)萬(wan)年(nian)時，盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)邊(bian)(bian)緣(yuan)(yuan)山(shan)(shan)(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)(di)(di)(di)迅(xun)速隆升，長(chang)(chang)(chang)江中(zhong)(zhong)(zhong)(zhong)上(shang)游水(shui)系開始溝通。盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)內(nei)湖水(shui)東瀉奠(dian)定了(le)現今之(zhi)地(di)(di)(di)(di)(di)(di)(di)(di)(di)貌形態。盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)邊(bian)(bian)緣(yuan)(yuan)多低山(shan)(shan)(shan)(shan)(shan)(shan)和(he)(he)中(zhong)(zhong)(zhong)(zhong)山(shan)(shan)(shan)(shan)(shan)(shan)，山(shan)(shan)(shan)(shan)(shan)(shan)勢(shi)陡峻，發(fa)源盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)邊(bian)(bian)緣(yuan)(yuan)山(shan)(shan)(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)(di)(di)(di)的(de)(de)河(he)流(liu)大(da)多為(wei)(wei)(wei)(wei)“V”型谷，嶺谷高(gao)差都逾500～1 000米(mi)(mi)， 地(di)(di)(di)(di)(di)(di)(di)(di)(di)表崎(qi)嶇，故(gu)歷史上(shang)就(jiu)有“蜀道難，難于(yu)上(shang)青天”之(zhi)說。山(shan)(shan)(shan)(shan)(shan)(shan)脊海(hai)拔(ba)大(da)多在(zai)2000～3000米(mi)(mi)，西(xi)(xi)北(bei)部(bu)與西(xi)(xi)部(bu)可(ke)超(chao)過(guo)3000～4000米(mi)(mi)，如龍(long)門山(shan)(shan)(shan)(shan)(shan)(shan)4984米(mi)(mi)，峨(e)眉山(shan)(shan)(shan)(shan)(shan)(shan)3099米(mi)(mi)，小相嶺4 791米(mi)(mi)。地(di)(di)(di)(di)(di)(di)(di)(di)(di)表廣泛出露古生代(dai)及(ji)(ji)其(qi)以(yi)(yi)前的(de)(de)石(shi)灰(hui)(hui)(hui)(hui)巖(yan)(yan)(yan)(yan)(yan)(yan)，其(qi)次為(wei)(wei)(wei)(wei)板巖(yan)(yan)(yan)(yan)(yan)(yan)、片巖(yan)(yan)(yan)(yan)(yan)(yan)、結晶灰(hui)(hui)(hui)(hui)巖(yan)(yan)(yan)(yan)(yan)(yan)、石(shi)英巖(yan)(yan)(yan)(yan)(yan)(yan)、砂泥(ni)(ni)巖(yan)(yan)(yan)(yan)(yan)(yan)和(he)(he)礫(li)巖(yan)(yan)(yan)(yan)(yan)(yan)，局(ju)部(bu)有花(hua)(hua)崗巖(yan)(yan)(yan)(yan)(yan)(yan)和(he)(he)玄武巖(yan)(yan)(yan)(yan)(yan)(yan)。石(shi)灰(hui)(hui)(hui)(hui)巖(yan)(yan)(yan)(yan)(yan)(yan)分布區(qu)可(ke)見石(shi)林、溶洞、暗河(he)、槽谷等(deng)(deng)喀斯特(te)地(di)(di)(di)(di)(di)(di)(di)(di)(di)貌，盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)南緣(yuan)(yuan)興(xing)(xing)文縣素有“石(shi)林洞鄉”之(zhi)稱(cheng)（見興(xing)(xing)文石(shi)林）。巫山(shan)(shan)(shan)(shan)(shan)(shan)十二峰和(he)(he)金佛(fo)山(shan)(shan)(shan)(shan)(shan)(shan)等(deng)(deng)名山(shan)(shan)(shan)(shan)(shan)(shan)主(zhu)要(yao)也由(you)石(shi)灰(hui)(hui)(hui)(hui)巖(yan)(yan)(yan)(yan)(yan)(yan)發(fa)育而成。由(you)石(shi)灰(hui)(hui)(hui)(hui)巖(yan)(yan)(yan)(yan)(yan)(yan)、玄武巖(yan)(yan)(yan)(yan)(yan)(yan)、花(hua)(hua)崗巖(yan)(yan)(yan)(yan)(yan)(yan)等(deng)(deng)組成的(de)(de)峨(e)眉山(shan)(shan)(shan)(shan)(shan)(shan)及(ji)(ji)由(you)砂泥(ni)(ni)巖(yan)(yan)(yan)(yan)(yan)(yan)、礫(li)巖(yan)(yan)(yan)(yan)(yan)(yan)組成的(de)(de)青城山(shan)(shan)(shan)(shan)(shan)(shan)，素有“峨(e)眉天下秀(xiu)”、“青城天下幽(you)”之(zhi)稱(cheng)，為(wei)(wei)(wei)(wei)中(zhong)(zhong)(zhong)(zhong)國著(zhu)名游覽勝地(di)(di)(di)(di)(di)(di)(di)(di)(di)。盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)底部(bu)海(hai)拔(ba)多數在(zai)250～700米(mi)(mi)，地(di)(di)(di)(di)(di)(di)(di)(di)(di)勢(shi)東南傾，盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)內(nei)各河(he)流(liu)均由(you)邊(bian)(bian)緣(yuan)(yuan)山(shan)(shan)(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)(di)(di)(di)匯聚盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)底部(bu)的(de)(de)長(chang)(chang)(chang)江干流(liu)，形成向(xiang)心狀水(shui)系。地(di)(di)(di)(di)(di)(di)(di)(di)(di)表為(wei)(wei)(wei)(wei)大(da)面積的(de)(de)中(zhong)(zhong)(zhong)(zhong)生代(dai)紫(zi)紅(hong)色(se)砂巖(yan)(yan)(yan)(yan)(yan)(yan)與泥(ni)(ni)巖(yan)(yan)(yan)(yan)(yan)(yan)所覆蓋(gai)，故(gu)稱(cheng)為(wei)(wei)(wei)(wei)“紅(hong)層盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)”，是中(zhong)(zhong)(zhong)(zhong)國中(zhong)(zhong)(zhong)(zhong)生代(dai)陸相紅(hong)層分布最集中(zhong)(zhong)(zhong)(zhong)地(di)(di)(di)(di)(di)(di)(di)(di)(di)區(qu)。四川(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)為(wei)(wei)(wei)(wei)丘陵(ling)性盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)，底部(bu)以(yi)(yi)丘陵(ling)為(wei)(wei)(wei)(wei)主(zhu)，次為(wei)(wei)(wei)(wei)低山(shan)(shan)(shan)(shan)(shan)(shan)和(he)(he)平(ping)原(yuan)。
四川(chuan)盆(pen)地(di)屬揚(yang)子陸臺(tai)一(yi)部(bu)分，稱為(wei)四川(chuan)陸臺(tai)，屬較穩定的(de)(de)(de)地(di)區，但仍(reng)經(jing)過兩次(ci)(ci)大規模的(de)(de)(de)海(hai)(hai)浸。第(di)一(yi)次(ci)(ci)從5億(yi)多(duo)年(nian)前的(de)(de)(de)寒武紀(ji)(ji)(ji)開始，延續到3.7億(yi)多(duo)年(nian)的(de)(de)(de)志留紀(ji)(ji)(ji)，不(bu)斷下陷(xian)(xian)成(cheng)(cheng)了海(hai)(hai)洋盆(pen)地(di)，志留紀(ji)(ji)(ji)時(shi)發生加里東運(yun)動，除了西部(bu)的(de)(de)(de)龍門山(shan)地(di)槽(cao)繼續下陷(xian)(xian)外(wai)，其余地(di)區上升(sheng)為(wei)陸。2.7億(yi)年(nian)前的(de)(de)(de)石炭紀(ji)(ji)(ji)末，發生范圍更大的(de)(de)(de)第(di)二次(ci)(ci)海(hai)(hai)浸，盆(pen)地(di)再次(ci)(ci)為(wei)海(hai)(hai)洋占據(ju)。二疊紀(ji)(ji)(ji)時(shi)海(hai)(hai)陸交替，形成(cheng)(cheng)重慶附近(jin)的(de)(de)(de)南酮、松藻、天府等煤礦。二疊紀(ji)(ji)(ji)末，盆(pen)地(di)西部(bu)巖漿噴出，峨眉(mei)山(shan)小金(jin)頂及清音閣(ge)一(yi)帶的(de)(de)(de)玄武巖就在這時(shi)生成(cheng)(cheng)。
距(ju)今1.9億年的(de)(de)三疊(die)紀，“印支運動”使盆地邊緣逐(zhu)(zhu)漸隆(long)起成山，被(bei)海水(shui)淹沒(mei)的(de)(de)地區(qu)(qu)逐(zhu)(zhu)漸上升成陸，由海盆轉為湖盆。當時湖水(shui)幾乎占據現(xian)今四川盆地的(de)(de)全境，稱為“蜀湖”，從此(ci)結束了海浸的(de)(de)歷史。在(zai)中生(sheng)代漫長的(de)(de)1億多年里，盆地氣(qi)候溫暖濕潤(run)，到處生(sheng)長蕨(jue)類、蘇鐵和(he)裸子植物，是又一個成煤期，永榮煤礦即在(zai)三疊(die)紀和(he)侏羅紀時形成。東起長壽、墊(dian)江，西到江油、邛崍，北抵(di)大(da)巴山麓，南到貴州赤水(shui)，還(huan)是天然氣(qi)富集區(qu)(qu)。這一時期爬行動物恐(kong)龍稱霸一時。1957年在(zai)合州發現(xian)的(de)(de)“合州馬門溪龍”身長22米(mi)，高3.5米(mi)，是中國亞(ya)洲最大(da)和(he)最完整的(de)(de)恐(kong)龍化石。
7000萬年前的(de)(de)(de)(de)(de)(de)白堊紀(ji)末期，發(fa)生又一(yi)次強烈的(de)(de)(de)(de)(de)(de)地(di)(di)(di)殼運(yun)動“燕山運(yun)動”。盆(pen)(pen)(pen)地(di)(di)(di)四(si)周山地(di)(di)(di)繼續(xu)隆(long)起(qi)，同時產生不(bu)少大(da)(da)(da)斷(duan)層，如西(xi)(xi)部(bu)的(de)(de)(de)(de)(de)(de)龍門山大(da)(da)(da)斷(duan)層和(he)東部(bu)的(de)(de)(de)(de)(de)(de)華瑩山大(da)(da)(da)斷(duan)層，把盆(pen)(pen)(pen)地(di)(di)(di)分為(wei)(wei)(wei)(wei)三(san)部(bu)分。蜀湖(hu)縮(suo)小為(wei)(wei)(wei)(wei)僅(jin)有2萬平(ping)方公里的(de)(de)(de)(de)(de)(de)蜀湖(hu)。封閉(bi)的(de)(de)(de)(de)(de)(de)盆(pen)(pen)(pen)地(di)(di)(di)地(di)(di)(di)形(xing)(xing)及急劇(ju)縮(suo)小的(de)(de)(de)(de)(de)(de)水面，使氣候逐漸變得(de)干熱(re)，沉(chen)積物由海(hai)相(xiang)、海(hai)陸(lu)(lu)交替相(xiang)變為(wei)(wei)(wei)(wei)陸(lu)(lu)相(xiang)，大(da)(da)(da)量(liang)風化、侵(qin)蝕(shi)、剝蝕(shi)的(de)(de)(de)(de)(de)(de)物質(zhi)在盆(pen)(pen)(pen)地(di)(di)(di)堆(dui)積了(le)數千米(mi)厚，形(xing)(xing)成紅色(se)和(he)紫(zi)紅色(se)的(de)(de)(de)(de)(de)(de)砂、泥(ni)、頁(ye)巖。裸子植物不(bu)斷(duan)衰(shuai)退，恐龍滅絕了(le)。內陸(lu)(lu)湖(hu)泊(bo)在干燥條件下，經(jing)強烈蒸(zheng)發(fa)，濃(nong)度增大(da)(da)(da)，鹽(yan)分不(bu)斷(duan)積累，形(xing)(xing)成鹽(yan)湖(hu)，后(hou)來(lai)泥(ni)沙掩埋而保存于地(di)(di)(di)層之中，經(jing)過漫(man)長的(de)(de)(de)(de)(de)(de)地(di)(di)(di)質(zhi)作用形(xing)(xing)成巖層，自貢(gong)一(yi)帶是(shi)著名(ming)的(de)(de)(de)(de)(de)(de)井鹽(yan)產地(di)(di)(di)。 2000多萬年前的(de)(de)(de)(de)(de)(de)新(xin)第(di)三(san)紀(ji)，受喜馬拉(la)雅造山運(yun)動的(de)(de)(de)(de)(de)(de)影響。距今(jin)二(er)、三(san)百萬年的(de)(de)(de)(de)(de)(de)第(di)四(si)紀(ji)，地(di)(di)(di)殼再次發(fa)生構造運(yun)動。從而，四(si)川盆(pen)(pen)(pen)地(di)(di)(di)由內流(liu)盆(pen)(pen)(pen)地(di)(di)(di)變為(wei)(wei)(wei)(wei)外流(liu)陸(lu)(lu)盆(pen)(pen)(pen)，由封閉(bi)的(de)(de)(de)(de)(de)(de)內流(liu)區變為(wei)(wei)(wei)(wei)外流(liu)區，由以堆(dui)積為(wei)(wei)(wei)(wei)主(zhu)變為(wei)(wei)(wei)(wei)侵(qin)蝕(shi)為(wei)(wei)(wei)(wei)主(zhu)，經(jing)歷了(le)海(hai)盆(pen)(pen)(pen)——湖(hu)盆(pen)(pen)(pen)——陸(lu)(lu)盆(pen)(pen)(pen)的(de)(de)(de)(de)(de)(de)滄桑之變。 第(di)四(si)紀(ji)是(shi)冰(bing)川廣布的(de)(de)(de)(de)(de)(de)時代，盆(pen)(pen)(pen)地(di)(di)(di)西(xi)(xi)北山地(di)(di)(di)發(fa)育(yu)大(da)(da)(da)量(liang)冰(bing)川。冰(bing)川消融后(hou)，大(da)(da)(da)量(liang)沉(chen)積物由岷江、沱江等攜帶，堆(dui)積在西(xi)(xi)部(bu)的(de)(de)(de)(de)(de)(de)凹陷區，即以前的(de)(de)(de)(de)(de)(de)蜀湖(hu)之中，最終形(xing)(xing)成了(le)成都平(ping)原。 四(si)川盆(pen)(pen)(pen)地(di)(di)(di)地(di)(di)(di)貌豐富，平(ping)原7%，丘陵52%，低(di)山41%。
四川(chuan)盆地中(zhong)植物(wu)近萬種，古(gu)老而特有種之多為中(zhong)國其(qi)他(ta)地區所不(bu)及。在盆地邊緣(yuan)山(shan)(shan)地及盆東平行嶺谷尚可見(jian)(jian)水杉(shan)(shan)、銀杉(shan)(shan)、鵝掌楸、檫木(mu)(mu)(mu)、三尖(jian)杉(shan)(shan)、珙(gong)桐、水青樹、連香樹、領春木(mu)(mu)(mu)、金錢槭(qi)、蠟(la)梅(mei)、杜仲、紅豆杉(shan)(shan)、鐘萼(e)木(mu)(mu)(mu)、福建柏(bo)、穗花杉(shan)(shan)、崖柏(bo)、木(mu)(mu)(mu)瓜紅等珍(zhen)稀孑遺植物(wu)與特有種。在濕熱河谷可見(jian)(jian)桫欏(luo)、小羽桫欏(luo)、烏毛蕨(jue)、華南(nan)紫萁、里白(bai)等古(gu)熱帶(dai)孑遺植物(wu)。 四川(chuan)盆地的(de)地帶(dai)性植被是亞(ya)熱帶(dai)常(chang)綠(lv)闊(kuo)葉(xie)(xie)林(lin)(lin)，其(qi)代表(biao)樹種有栲(kao)樹、峨眉栲(kao)、刺果米(mi)櫧(zhu)、青岡、曼(man)青岡、包石櫟、華木(mu)(mu)(mu)荷、大(da)(da)包木(mu)(mu)(mu)荷、四川(chuan)大(da)(da)頭(tou)茶(cha)、楨楠、潤(run)楠等，海拔一般(ban)情(qing)況下在1600～1 800米(mi)以下。其(qi)次有馬尾松(song)、杉(shan)(shan)木(mu)(mu)(mu)、柏(bo)木(mu)(mu)(mu)組成 的(de)亞(ya)熱帶(dai)針葉(xie)(xie)林(lin)(lin)及竹林(lin)(lin)。 邊緣(yuan)山(shan)(shan)地從下而上是常(chang)綠(lv)闊(kuo)葉(xie)(xie)林(lin)(lin)、常(chang)綠(lv)闊(kuo)葉(xie)(xie)與落葉(xie)(xie)闊(kuo)葉(xie)(xie)混交林(lin)(lin)，寒溫帶(dai)山(shan)(shan)地針葉(xie)(xie)林(lin)(lin)，局部(bu)有亞(ya)高山(shan)(shan)灌叢草甸(dian)。
四川(chuan)(chuan)盆(pen)地(di)(di)(di)(di)是中(zhong)(zhong)國動物(wu)(wu)種類最多、最齊全的(de)(de)(de)地(di)(di)(di)(di)區(qu)之一(yi)(yi)。據統計，除魚類外，盆(pen)地(di)(di)(di)(di)底(di)部共(gong)有(you)(you)動物(wu)(wu)417種，盆(pen)地(di)(di)(di)(di)西(xi)(xi)緣(yuan)、北(bei)緣(yuan)和南緣(yuan)山地(di)(di)(di)(di)分(fen)別為487種、317種與288種，其中(zhong)(zhong)經濟動物(wu)(wu)均占(zhan)一(yi)(yi)半以上。盆(pen)地(di)(di)(di)(di)西(xi)(xi)緣(yuan)山地(di)(di)(di)(di)是中(zhong)(zhong)國特有(you)(you)而古(gu)老(lao)動物(wu)(wu)保(bao)存最好、最集中(zhong)(zhong)的(de)(de)(de)地(di)(di)(di)(di)區(qu)，屬于一(yi)(yi)類保(bao)護動物(wu)(wu)的(de)(de)(de)有(you)(you)大熊貓、金絲猴(hou)(hou)、扭角羚(ling)(ling)、灰金絲猴(hou)(hou)、白(bai)唇鹿(lu)等(deng)(deng)(deng)。還有(you)(you)珍貴特有(you)(you)動物(wu)(wu)小熊貓、雪豹、鬣羚(ling)(ling)、短尾猴(hou)(hou)、獼猴(hou)(hou)、毛冠鹿(lu)、水獺及(ji)(ji)鴛鴦、血雉、紅腹(fu)角雉、綠尾虹雉、白(bai)腹(fu)錦雞、紅腹(fu)錦雞等(deng)(deng)(deng)。 盆(pen)地(di)(di)(di)(di)西(xi)(xi)緣(yuan)的(de)(de)(de)平(ping)武、青川(chuan)(chuan)、北(bei)川(chuan)(chuan)、寶興、天全、洪雅(ya)、馬邊(bian)等(deng)(deng)(deng)地(di)(di)(di)(di)，均為中(zhong)(zhong)國大熊貓的(de)(de)(de)主要分(fen)布區(qu)。已設(she)立(li)唐家河(he)、王朗、臥(wo)(wo)龍（見臥(wo)(wo)龍自然(ran)保(bao)護區(qu)）、蜂桶寨、喇(la)叭河(he)等(deng)(deng)(deng)7處大熊貓、金絲猴(hou)(hou)等(deng)(deng)(deng)自然(ran)保(bao)護區(qu)。 酉陽、馬邊(bian)、平(ping)武等(deng)(deng)(deng)盆(pen)地(di)(di)(di)(di)邊(bian)緣(yuan)山地(di)(di)(di)(di)溪溝中(zhong)(zhong)的(de)(de)(de)大鯢及(ji)(ji)長江、金沙(sha)江中(zhong)(zhong)的(de)(de)(de)中(zhong)(zhong)華鱘、白(bai)鱘也為四川(chuan)(chuan)所特有(you)(you)，均屬國家保(bao)護動物(wu)(wu)。
四川(chuan)(chuan)盆地(di)有煤、鐵、天然氣、石油、鹽、芒硝、石膏、磷、硫、鋁、金、銅(tong)、錳、石墨(mo)、汞等礦產資(zi)源，其中(zhong)(zhong)天然氣、芒硝為全中(zhong)(zhong)國(guo)之冠(guan)，并有中(zhong)(zhong)國(guo)重要的鍶礦。川(chuan)(chuan)東(dong)北是世界最(zui)大的天然氣富集區之一，川(chuan)(chuan)中(zhong)(zhong)和南充(chong)等地(di)鹽巖礦儲量很(hen)大。
四(si)川盆(pen)地(di)(di)地(di)(di)形閉塞，由于(yu)北(bei)(bei)部(bu)秦嶺阻擋(dang)冷空氣(qi)，冬(dong)季氣(qi)溫高于(yu)同(tong)緯(wei)(wei)度(du)其(qi)他地(di)(di)區。最冷月(yue)北(bei)(bei)部(bu)均(jun)溫3～5℃，南(nan)(nan)部(bu)5~8℃，較同(tong)緯(wei)(wei)度(du)的上(shang)海、湖北(bei)(bei)、安(an)徽及緯(wei)(wei)度(du)偏南(nan)(nan)的貴(gui)州高1～4℃。盆(pen)地(di)(di)北(bei)(bei)部(bu)極端最低(di)溫-8～-5℃，南(nan)(nan)部(bu)-5℃~-2℃。霜(shuang)(shuang)(shuang)雪少見，年(nian)無霜(shuang)(shuang)(shuang)期長(chang)280～350天(tian)，同(tong)緯(wei)(wei)度(du)上(shang)的武漢冬(dong)天(tian)卻霜(shuang)(shuang)(shuang)雪不斷(duan)，盆(pen)地(di)(di)位于(yu)長(chang)江(jiang)河谷中(zhong)的長(chang)寧(ning)全年(nian)無霜(shuang)(shuang)(shuang)。 盆(pen)地(di)(di)各地(di)(di)夏(xia)(xia)季始于(yu)5月(yue)底，終于(yu)9月(yue)中(zhong)旬，夏(xia)(xia)長(chang)4個月(yue)，溫度(du)上(shang)東高西(xi)低(di)。盆(pen)地(di)(di)西(xi)部(bu)夏(xia)(xia)天(tian)平均(jun)氣(qi)溫約(yue)25℃，較同(tong)緯(wei)(wei)度(du)的上(shang)海、武漢等城市偏低(di)3-4度(du)，但濕度(du)較大，所以悶熱難忍(ren)。
東(dong)部最熱月(yue)氣(qi)溫(wen)(wen)高(gao)(gao)(gao)達26～29℃，長(chang)江河谷(gu)局地(di)達到30℃。盛夏(xia)連(lian)晴高(gao)(gao)(gao)溫(wen)(wen)天(tian)氣(qi)又造成盆(pen)(pen)地(di)東(dong)南(nan)(nan)(nan)部嚴重的(de)夏(xia)伏旱。盆(pen)(pen)地(di)氣(qi)溫(wen)(wen)東(dong)南(nan)(nan)(nan)高(gao)(gao)(gao)西北(bei)低(di)，盆(pen)(pen)底(di)高(gao)(gao)(gao)邊緣低(di)； 各地(di)年(nian)均溫(wen)(wen)16～18℃。10℃以上(shang)活動積(ji)溫(wen)(wen)4500～6000℃，持續期8～9個月(yue)，屬中(zhong)亞熱帶(dai)(dai)。東(dong)南(nan)(nan)(nan)部的(de)長(chang)江河谷(gu)積(ji)溫(wen)(wen)超(chao)過6000℃，相當于中(zhong)國南(nan)(nan)(nan)嶺以南(nan)(nan)(nan)的(de)南(nan)(nan)(nan)亞熱帶(dai)(dai)氣(qi)候。盆(pen)(pen)地(di)氣(qi)溫(wen)(wen)東(dong)高(gao)(gao)(gao)西低(di)，南(nan)(nan)(nan)高(gao)(gao)(gao)北(bei)低(di)，盆(pen)(pen)底(di)高(gao)(gao)(gao)而(er)邊緣低(di)，等溫(wen)(wen)線(xian)分布(bu)呈現同(tong)心圓(yuan)狀。盆(pen)(pen)地(di)邊緣山(shan)地(di)氣(qi)溫(wen)(wen)具有垂直分布(bu)特點，如峨眉山(shan)、金(jin)佛山(shan)海拔升高(gao)(gao)(gao)百米，氣(qi)溫(wen)(wen)遞減(jian)0.55℃和0.61℃。峨眉山(shan)頂年(nian)均溫(wen)(wen)僅3℃，10℃以上(shang)活動積(ji)溫(wen)(wen)586℃，氣(qi)候上(shang)相當于寒(han)溫(wen)(wen)帶(dai)(dai)和亞寒(han)帶(dai)(dai)。
四川盆(pen)(pen)(pen)地年(nian)降(jiang)水(shui)(shui)量(liang)1000～1300毫米(mi)，盆(pen)(pen)(pen)地邊緣(yuan)山地降(jiang)水(shui)(shui)十分(fen)充沛(pei)，如(ru)樂山和雅安間的西緣(yuan)山地年(nian)降(jiang)水(shui)(shui)量(liang)為1 500～1800毫米(mi)，為中(zhong)國(guo)突出的多雨(yu)區，有(you)“華西雨(yu)屏”之稱。但(dan)冬干、春旱、夏澇(lao)、秋綿雨(yu)，年(nian)內分(fen)配不(bu)均，70～75%的雨(yu)量(liang)集中(zhong)于6～10月(yue)。最大日降(jiang)水(shui)(shui)量(liang)可達(da)300～500毫米(mi)。“巴山夜(ye)雨(yu)”自古聞名，夜(ye)雨(yu)占總(zong)雨(yu)量(liang)的60～70%以(yi)上。盆(pen)(pen)(pen)地區霧大濕(shi)重，云低陰(yin)天多。峨眉山、金佛山是中(zhong)國(guo)霧日最多地區之一，年(nian)相對(dui)濕(shi)度之高也(ye)為中(zhong)國(guo)之冠。盆(pen)(pen)(pen)地年(nian)日照僅(jin)900～1300小時，年(nian)太(tai)陽輻(fu)射量(liang)為370～420千焦耳(er)/平方(fang)厘米(mi)，均為中(zhong)國(guo)最低值，故有(you)“蜀(shu)犬(quan)吠日”之說。
